1
- (added to adjectives, participles, and their derivatives) denoting the absence of a quality or state; not［用于形容词、分词及其派生词前］表示“否”, “非”：
unabashed
unacademic
unrepeatable.
1.1
- the reverse of (usually with an implication of approval or disapproval, or with another special connotation)表示“相反”, “对立”：
unselfish
unprepossessing
unworldly.
2
- (added to nouns) a lack of用于名词前表示“缺少”：
unrest
untruth.
USAGE
The prefixes un- and non- both mean 'not', but there is often a distinction in terms of emphasis. un- tends to be stronger and less neutral than non-： consider the differences between unacademic and non-academic, for example （his language was refreshingly unacademic; a non-academic life suits him）.
词源
Old English, of Germanic origin: from an IndoEuropean root shared by Latin in- and Greek a-.
added to verbs 动词前缀。
1
- denoting the reversal or cancellation of an action or state表示“做相反的动作”或“取消”：
untie
unsettle.
2
- denoting deprivation, separation, or reduction to a lesser state表示“免去”, “剥夺”, “使降级”：
unmask
unman.
2.1
- denoting release表示“除去”, “使自由”：
unburden.
unhand.
词源
Old English un-, on-, of Germanic origin: related to Dutch ont- and German ent-.