- (added to adjectives or past participles) not
- unannounced — “not being announced”
- uneducated — “not educated”
- unattractive — “not attractive”
- unconstitutional — “not constitutional”
- (added to nouns) absent; lacking; not; negative
- (added to nouns) contrary to or contrasted against traditional norms; unconventional; alternative
- (added to verbs and nouns to form verbs) reverse, opposite
- to undress — “to take one's clothes off”
- to unwind — “to reverse a winding”
- to unlock — “to undo the locking of”
- 1996, Diane Warren (writer), Toni Braxton (singer), “Un-Break My Heart”, Secrets, LaFace
- Un-cry these tears I cried so many nights / Un-break my heart
- release, free, remove, extract.
- to uncage — “to release from a cage”
- to untangle — “to remove the tangling of”
- Used to form temporary names of elements (such as unbiunium) whose existence has been predicted, and have not yet been given a trivial name.
- Used to form large numbers as the first in the sequence.