Undercover describes work done in secret, where someone hides who they really are in order to gather information or catch criminals. The classic case is a police officer who pretends to be a drug buyer for months, but the word also covers journalists, government agents and investigators — 'an undercover reporter filmed conditions in the factory'.

Undercover describes work done in secret undercover 是指秘密進行的工作, where someone hides who they really are某人隱藏自己的真實身分 in order to gather information or catch criminals為了蒐集情報或抓犯人. The classic case is a police officer who pretends to be a drug buyer for months最典型的例子是警察假扮買毒者臥底好幾個月, but the word also covers journalists, government agents and investigators但這個字也涵蓋記者、政府探員和調查員 — 'an undercover reporter filmed conditions in the factory'像「an undercover reporter filmed conditions in the factory」

Two things matter about the meaning. First, it is not just secret; it involves a false identity, actually living as someone else. Second, it is a word about legitimate investigation, so it usually sounds brave or clever rather than dishonest — a spy for a criminal gang would more likely be called a 'mole' or 'plant'.

Two things matter about the meaning這個意思有兩件事很重要. First第一, it is not just secret它不只是「秘密」而已; it involves a false identity它牽涉到假身分, actually living as someone else真的以另一個人的身分生活. Second第二, it is a word about legitimate investigation這是個關於正當調查的字, so it usually sounds brave or clever rather than dishonest所以聽起來通常是勇敢或聰明，而不是不誠實 — a spy for a criminal gang如果是替犯罪集團當間諜的人 would more likely be called a 'mole' or 'plant'比較可能被稱作「mole」或「plant」

Grammatically it works both as an adjective before a noun ('an undercover agent', 'an undercover operation') and as an adverb after a verb ('she went undercover for six months', 'he worked undercover'). 'Go undercover' is the phrase students should memorise.

Grammatically在文法上 it works both as an adjective before a noun它可以當形容詞放在名詞前面（'an undercover agent'「an undercover agent」、'an undercover operation'「an undercover operation」）and as an adverb after a verb也可以當副詞放在動詞後面（'she went undercover for six months'「she went undercover for six months」、'he worked undercover'「he worked undercover」）. 'Go undercover'「go undercover」 is the phrase students should memorise是學生應該背起來的片語

It can be used lightly and jokingly too — 'I went undercover at my son's school fair' — and that humorous use is common in English. It is not normally used for ordinary secrets: keeping a birthday present hidden is 'secret', not 'undercover'.

It can be used lightly and jokingly too它也可以輕鬆開玩笑地用 — 'I went undercover at my son's school fair'像「I went undercover at my son's school fair」 — and that humorous use is common in English這種幽默用法在英文裡很常見. It is not normally used for ordinary secrets它通常不用在一般的秘密上: keeping a birthday present hidden把生日禮物藏起來 is 'secret', not 'undercover'是「secret」，不是「undercover」