- (British English) (North American English undershirt)
a piece of underwear worn under a shirt, etc. next to the skin （衬衣等里面贴身穿的）背心，汗衫 a cotton vest 棉汗衫
Extra ExamplesTopics Clothes and Fashionb2What are you doing, standing there in your vest? 你穿着背心站在那里干什么？ standing there in vest and shorts 穿着背心短裤站在那
Oxford Collocations Dictionaryadjective- sleeveless
- string
- thermal
- …
- in your vest
a special piece of clothing that covers the upper part of the body 坎肩；（外面穿的）背心 a bullet-proof vest 防弹背心 a running vest 赛跑背心
Oxford Collocations Dictionaryadjective- bulletproof
- stab-proof
- Kevlar™
- …
- (North American English) (British English waistcoat)
a short piece of clothing with buttons down the front but no arms, usually worn over a shirt and under a jacket, often forming part of a man’s suit （西服的）背心 
wearing jeans and a leather vest 穿着牛仔裤和皮背心 He is smartly dressed in a suit complete with vest, tie and polished Gucci loafers. 他一身西装，很是光鲜，穿了背心、打了领带，脚上是擦得锃亮的古驰平底便鞋。
Oxford Collocations Dictionaryadjective- sleeveless
- matching
- denim
- …
Word Originlate Middle English (as a verb): from Old French vestu ‘clothed’, past participle of vestir, from Latin vestire; the noun (early 17th cent., denoting a loose outer garment) from French veste, via Italian from Latin vestis ‘garment’.