1 (used in adjectives, adverbs and nouns 用于构成形容词、副词及名词) not; the opposite of 不；相反: unable 不能够unconsciously 无意识untruth 不真实un-American activities(= against the interests of the US) 非美活动（即对美国利益不利的活动）

2 (used in verbs that describe the opposite of a process 用于构成动词，以表示相反的动作) unlock 开锁 · undo 解开unfold 摊开