Mandarin features lots of four-character “set phrases” that indicate a description, an emotion, a situation, etc. I find them fascinating, so I’m gathering the ones I come across as I go. I’ll put them here, in case others are curious, too.

四面八方 (simian-bāfāng) – All directions; all around

遮天蔽日 (zhētiān-bìrì) – hiding the sky and covering the earth; earth-shattering

震耳欲聋 (zhèn’ěr-yùlóng) – ear-splitting; deafening

剑拔弩张 (jiànbá-nǔzhāng) – a state of mutual hostility; with swords drawn and bows bent

滥杀无辜 (lànshā-wúgū) – wanton slaughter the innocent

螳臂当车 (tángbì-dāngchē) – a mantis trying to obstruct a chariot; overrate oneself and try to hold back an overwhelming force

自不量力 (zìbùliànglì) – overestimate one’s ability; not know one’s own limitations

铺天盖地 (pūtiān-gàidì) – eclipsing the sky and blanketing the earth; arriving in overwhelming quantities; all-pervasive

周而复始 (zhōu’érfùshǐ)  – The cycle comes back to the start; to move in circles

天下大乱 (tiānxià-dàluàn) – disorder under heaven; a state of great confusion; whole country in rebellion

不言不语 (bùyán-bùyǔ) – not say a word; keep silent

心事重重 (xīnshì-chóngchóng) – be laden with anxiety; be weighed down with caring

小心翼翼(xiǎoxīn-yìyì) – cautious, careful, prudent

习以为常 (xíyǐ-wéicháng) – accustomed to; inured to

臭名昭著 (chòumíng-zhāozhù) – of ill repute, notorious, infamous

血流成河 (xuèliú-chénghé) – blood flowing like a river—bloodbath; rivers of blood

不动声色 (bùdòng-shēngsè) – not a word or movement; stay calm and collected; not bat an eyelid; maintain one’s composure

瓢泼大雨 (piáopō-dàyǔ) – downpour; heavy rain; torrential rain (literal seems to be: a ladle splashing/spilling heavy rain…which is an image I love…)

尽收眼底 (jìnshōu-yǎndǐ) – take in the whole scene at once; have a panoramic view of something

名不见经传(míng bújiàn jīngzhuàn) – name not encountered in the classics; unknown, nobody (经传jīngzhuàn refers to the classics, especially the works of Confucius)

如雷贯耳 (rúléiguàn’ěr) – like thunder piercing the ear; reverberate like thunder; a well-known reputation

名满天下 (míngmǎntiānxià)– famous throughout the land; renowned far and wide

心口不一 (xīnkǒu-bùyī) – heart and mouth at variance; keeping one’s intentions to oneself; saying one thing and meaning another; be hypocritical

言不由衷 (yánbùyóuzhōng) – literal: words don’t follow inner feeling; say something without meaning it; to speak tongue in cheek

慢条斯理 (màntiáo-sīlǐ) – slowly, leisurely, unhurried

一蹶不振 (yījué-bùzhèn) – one stumble, unable to rise; collapse after a single setback; unable to recover after a setback or a minor hitch

以泪洗面 (yǐlèi-xǐmiàn) – bathe one’s face in tears; have a tearful face

囤积居奇 (túnjī-jūqí) – to hoard and profiteer

才华横溢 (cáihuá-héngyì) – brimming over with talent, esp. literary; exceptional talent; brilliant

见异思迁 (jiànyì-sīqiān) – literal: meet different, thinking changes; change at once on seeing something different; never satisfied with what one has

道貌岸然 (dàomào-ànrán) – pose as a person of high morals; sanctimonious

虚情假意 (xūqíng-jiǎyì) – false display of affection; hypocritical show of friendshup

居高临下 (jūgāo-línxià) – literal: to be in a high location, overlooking the scene; to occupy a commanding position; to assume a haughty attitude

不容置疑 (bùróng-zhìyí) – not open to doubt; not allow (or admit) doubt

名存实亡 (míngcún-shíwáng) – the name remains but the reality is gone; cease to exist except in name; exist in name only

口蜜腹剑 (kǒumì-fùjiàn) – honeyed words, a sword in the belly; honey-mouthed and dagger-hearted; hypocritical and murderous

佛口蛇心 (fókǒu-shéxīn) – Buddha’s mouth and viper’s heart; two-faced; honeyed words but evil intent

萍水相逢 (píngshuǐ-xiāngféng) – meet by chance like patches of drifting duck weed; strangers coming together by chance

处变不惊 (chǔbiàn-bùjīng) – literal: location/place/situation changes; not frightened; remain calm in the presence of volatile situations

魂飞魄散 (húnfēi-pòsàn) – literal: the soul flies away and scatters; figurative: to be scared out of one’s wits; be half dead with fright

不紧不慢 (bùjǐnbùmàn) – to take one’s time; unhurried

一动不动 (yīdòngbùdòng) – still, motionless

奄奄一息 (yǎnyǎn-yīxī) – at one’s last gasp; on the verge of death

伤天害理 (shāngtiān-hàilǐ) – bloody atrocities that cry to heaven; offend against heaven and reason; outrageous acts

赶尽杀绝 (gǎnjìn-shājué) – kill all; wipe out the whole lot; be ruthless; eradicate

永无止境 (yǒngwúzhǐjìng) – without end; never-ending

空无一人 (kōngwúyīrén) – not a soul in sight

自上而下 (zìshàng’erxià) – from above to below; from top to bottom; top-down

英姿飒爽 (yīngzī-sàshuǎng) – valiant and heroic in bearing; bold and brave; to carry oneself tall; valiant and formidable-looking

干脆利落 (gāncuì-lìluo) – be clear cut; come straight to the point; direct; without fooling around

罪魁祸首 (zuìkuí-huòshǒu) – chief culprit; arch criminal; main cause of a disaster

恶贯满盈 (èguàn-mǎnyíng) – literal: strung through and filled with evil; filled with extreme evil; guilty of countless crimes and deserve to come to judgement; steeped in evil and deserving damnation

来势汹汹 (láishìxiōngxiōng) – bear down menacingly

面不改色 (miànbùgǎisè) – not change color; remain calm; not bat an eyelid

杀气腾腾  (shāqì-téngténg) – murderous-looking, ferocious

公事公办 (gōngshì-gōngbàn) – business is business; do official business according to official principles; not let private affairs interfere with public duty

真心实意 (zhēnxīn-shíyì) – genuinely and sincerely; truly and whole-heartedly

十之八九 (shízhībājiǔ) – nine times out of ten; most likely

从中作梗 (cóngzhōng-zuògěng) – hinder somebody from carrying out a plan; place obstacles in the way

暗无天日 (ànwútiānrì) – complete darkness, total absence of justice

老老实实 (lǎolǎo-shíshí) – honestly, conscientiously, in earnest

百无聊赖 (bǎiwúliáolài) – bored to death; bored stiff; overcome with boredom

无缘无故 (wúyuán-wúgù) – without cause or reason; for no reason at all; without rhyme or reason

无欲无求 (wúyùwúqiú) – to be free of worldly desires and ambitions; to neither want nor seek (fame, profit, material gain, etc.)

鞠躬尽瘁 (jūgōng-jìncuì) – bend oneself to a task and exert oneself to the utmost; spare no effort in the performance of one’s duty

绘声绘色 (huìshēng-huìsè) – vivid; lively

怒发冲冠 (nùfà-chōngguān) – bristle with anger; be in a towering rage (or passion)

意味深长(yìwèi-shēncháng) – having deep meaning; pregnant with meaning; of profound significance

不足挂齿 (bùzú-guàchǐ) – not worth mentioning; nothing to speak of

毫发无伤 (háofàwúshāng) – unscathed, unharmed, without a scratch

礼尚往来 (lǐshàng-wǎnglái) – Courtesy demands reciprocity; deal with a man as he deals with you; pay a man back with his own coin; give as good as one gets

背道而驰 (bèidào’érchí) – run in the opposite direction; run counter to

微不足道 (wēibùzúdào) – too trivial or insignificant to mention; insignificant; inconsiderable

无论如何 (wúlùnrúhé) – in any case; at any rate; whatever happens

天诛地灭 (tiānzhū-dìmiè) – [in cursing or taking vows] be destroyed by heaven and earth; be struck down by the gods

暗无天日 (ànwútiānrì) – complete darkness, total absence of justice

兴致勃勃 (xìngzhì-bóbó) – full of zest; in high spirits

金刚怒目(jīngāng nùmù) – glare like a temple god; fierce-looking; ferocious glare

丧家之犬 (sàngjiā zhī quǎn) – stray cur

喜笑颜开 (xǐxiào yánkāi) – face wreathed in smiles; face lit up with pleasure; beam; radiant

没有意义 (mēiyǒu yìyì) – not to have any meaning; meaningless

相貌堂堂 (xiàngmào tángtáng) – dignified in appearance; impressive-looking

不疾不徐 (bùjíbùxú) – neither too fast nor too slow

冲锋陷阵 (chōngfēng-xiànzhèn) – charge and shatter enemy positions; charge the enemy lines; charge forward

虚心好学 (xūxīnhàoxué) – modest and studious

后知后觉 (hòuzhīhòujué) – to realize in hindsight; to realize belatedly; to be late to the party

迫不及待 (pòbùjídài) – very impatient; unable to hold back; too impatient to wait; anxious to do something

一动不动 (yīdòngbùdòng) – still

空空如也 (kōngkōngrúyě) – absolutely empty

干脆利落 (gāncuì-lìluo) – be clear-cut; come straight to the point; direct

拖泥带水 (tuōní-dàishuǐ) – messy; sloppy; slovenly

 以防万一 (yǐfáng-wànyī) – be prepared for all contingencies; be ready for any eventuality

来而不往非礼也 (lái ér bù wǎng fēi lǐ yě) – It is impolite not to reciprocate—one should return as good as one receives; it is only proper to repay in kind

溢于言表  (yìyúyánbiǎo) – (of feelings) show clearly in one’s words and manner

指名道姓 (zhǐmíng-dàoxìng) – mention somebody by name; name names

口是心非 (kǒushì-xīnfēi) – say yes and mean no; say one thing and mean another; double-faced

迫不及待 (pòbùjídài) – very impatient; unable to hold back; too impatient to wait; anxious to do something

玩世不恭 (wánshì-bùgōng) – thumb one’s nose at the world; cynical; indifferent

不翼而飞 (bùyì’érfēi) – disappear without a trace; vanish into thin air

海市蜃楼 (hǎishì-shènlóu) – castle in the air, illusion; mirage

冷眼旁观 (lěngyǎn-pángguān) – look on with a cold eye; watch critically

天下大乱 (tiānxià-dàluàn) – go disorder under heaven—a state of great confusion

恶贯满盈 (èguàn-mǎnyíng) – be guilty of countless crimes and deserve to come to judgement; be steeped in evil and deserve damnation

狗改不了吃屎 (gǒugǎibùliǎochīshǐ) – lit. a dog can’t stop himself from eating his own shit; fig. bad habits are hard to change

满盘皆输 (mǎnpánjiēshū) – One careless move and the whole game is lost

所作所为 (suǒzuò-suǒwéi) – one’s behavior or conduct

毫无顾忌 (háowú-gùjì) – without scruples; have no scruples

胡说八道 (húshuō-bādào) – talk nonsense; sheer nonsense; rubbish

痛心疾首 (tòngxīn-jíshóu) – with bitter hatred; bitterness

图谋不轨 (túmóu-bùguǐ) – plot something unlawful; engage in conspiratorial activities

包藏祸心 (bāocáng-huòxīn) – harbor evil intentions; malicious

 知无不言，言无不尽 (zhī wú bù yán, yán wú bù jìn) – say all you know and say it without remorse

作恶多端 (zuò’èduōduān) – do all kinds of evil; steeped in iniquity

一拍两散 (yīpāiliǎngsàn) – (of marriage or business partners) to break up; separate

左思右想 (zuǒsī-yòuxiǎng) – think over from different angles—turn something over in one’s mind

心满意足 (xīnmǎn-yìzú) – be perfectly content (or satisfied)

毕恭毕敬 (bìgōng-bìjìng) – reverent and respectful; extremely deferential

求之不得 (qiúzhī-bùdé) – all one could wish for; most welcome

打定主意 (dǎdìnng zhǔyi) – make up one’s mind

说不出口 (shuōbuchūkǒu) – find it hard to speak out; unutterable; unspeakable

愁眉不展 (chóuméi-bùzhǎn) – with a worried frown; with knitted brows

愁眉苦脸 (chóuméi-kǔliǎn) – wear a worried look; pull a long face

心事重重 (xīnshì-chóngchóng) – be laden with anxiety; to have a lot on one’s mind

浑浑噩噩 (húnhún’è’è) – muddle-headed and ignorant