| 四环素 | sì huán sù | tetracycline |
| 四碳糖 | sì tàn táng | tetrose (CH20)4, monosaccharide with four carbon atoms |
| 四级 | sì jí | grade 4; fourth class; category D |
| 四级士官 | sì jí shì guān | sergeant first class |
| 四维 | sì wéi | the four social bonds: propriety, justice, integrity and honour; see 礼义廉耻; the four directions; the four limbs (Chinese medicine); four-dimensional |
| 四维时空 | sì wéi shí kōng | four dimensional space-time (in relativity) |
| 四维空间 | sì wéi kōng jiān | four dimensional space (math.) |
| 四圣谛 | sì shèng dì | the Four Noble Truths (Buddhism); see also 四谛 and 苦集灭道 |
| 四脚朝天 | sì jiǎo cháo tiān | four legs facing the sky (idiom); flat on one's back |
| 四脚蛇 | sì jiǎo shé | lizard; common spoken equivalent of 蜥蜴 |
| 四旧 | sì jiù | the Four Olds (target of the Cultural Revolution) |
| 四号电池 | sì hào diàn chí | AAA battery (Taiwan); PRC equivalent: 七号电池 |
| 四角形 | sì jiǎo xíng | square; quadrilateral |
| 四角柱体 | sì jiǎo zhù tǐ | cuboid; rectangular prism (math.) |
| 四角号码 | sì jiǎo hào mǎ | four corner code (input method for Chinese characters) |
| 四角裤 | sì jiǎo kù | boxer shorts |
| 四谛 | sì dì | the Four Noble Truths (Budd.), covered by the acronym 苦集滅道: all life is suffering 苦, the cause of suffering is desire 集, emancipation comes only by eliminating passions 灭, the way 道 to emancipation is the Eight-fold Noble Way 八正道 |
| 四轮马车 | sì lún mǎ chē | chariot |
| 四轮驱动 | sì lún qū dòng | four wheel drive |
| 四近 | sì jìn | nearby |
| 四郊 | sì jiāo | suburb; outskirts (of town) |
| 四部曲 | sì bù qǔ | tetralogy |
| 四重奏 | sì chóng zòu | quartet (musical ensemble) |
| 四门轿车 | sì mén jiào chē | sedan (motor car) |
| 四灵 | sì líng | four divinities; four divine emperors; four mythical creatures symbolic of propsperity and longevity, namely phoenix 凤, turtle 龟, dragon 龙, Chinese unicorn 麒麟; also 四象, the four division of the sky |
| 四面楚歌 | sì miàn chǔ gē | lit. on all sides, the songs of Chu (idiom); fig. surrounded by enemies, isolated and without help |
| 四头肌 | sì tóu jī | quadriceps muscle group; thigh muscles |
| 四体 | sì tǐ | one's four limbs; two arms and two legs |
四体不勤，
五谷不分 | sì tǐ bù qín ,
wǔ gǔ bù fēn | never move your four limbs, can't distinguish the five crops (idiom); living as a parasite |
| 大四 | dà sì | fourth-year university student |
| 宋四大书 | Sòng sì dà shū | Four great compilations of Northern Song dynasty, namely: Extensive records of the Taiping era (978) 太平广记, Imperial readings of the Taiping era 太平御览, Prime tortoise of the record bureau 册府元龟, Finest blossoms in the garden of literature 文苑英华 |
| 宋四家 | Sòng sì jiā | four famous Song calligraphers, namely: Su Shi 苏轼, Huang Tingjian 黄庭坚, Mi Fei 米芾 and Cai Xiang 蔡襄 |
| 巴三览四 | bā sān lǎn sì | to talk about this and that (idiom); to ramble incoherently |
| 廿四史 | niàn sì shǐ | twenty four dynastic histories (or 25 or 26 in modern editions); same as 二十四史 |
| 张三李四 | Zhāng sān Lǐ sì | Zhang and Li (idiom); Zhang with tight trousers and Li with wide hat; Tom, Dick and Harry |
张三，
李四，
王五，
赵六 | Zhāng sān ,
Lǐ sì ,
Wáng wǔ ,
Zhào liù | four proverbial names; Tom, Dick and Harry |
| 志在四方 | zhì zài sì fāng | to aspire to travel far and make one’s mark (idiom) |
| 披头四乐团 | Pī tóu sì yuè tuán | The Beatles |
| 挑三窝四 | tiǎo sān wō sì | to sow discord everywhere |
| 推三阻四 | tuī sān zǔ sì | to use all sorts of excuses |
| 扬名四海 | yáng míng sì hǎi | known throughout the country (idiom); world-famous |
| 放之四海而皆准 | fàng zhī sì hǎi ér jiē zhǔn | appropriate to any place and any time (idiom); universally applicable; a panacea |
| 文房四宝 | wén fáng sì bǎo | Four Treasures of the Study, namely 笔, 墨, 纸 and 砚; the essentials of calligraphy and scholarship (idiom) |
| 星期四 | xīng qī sì | Thursday |
| 本周四 | běn zhōu sì | this Thursday |
| 李四 | Lǐ Sì | Li Si, name for an unspecified person, second of a series of three: 张三, 李四, 王五 Tom, Dick and Harry |
| 李四光 | Lǐ Sì guāng | Li Siguang (1889-1971), Mongol-born, Japanese trained geologist, prominent in early PRC oil exploration |
| 板板六十四 | bǎn bǎn liù shí sì | unaccommodating; rigid |
| 核四级共振 | hé sì jí gòng zhèn | nuclear quadrupole resonance (physics) |
| 横三竖四 | héng sān shù sì | in disorder; in a tremendous mess |
