Psychiatry.an unconscious defense mechanism through which an attempt is made to reverse a psychologically unacceptable act by doing its opposite, usually repetitiously, in order to relieve anxiety.
a screen or mat covered with a dark material for shielding a camera lens from excess light or glare.
a chattering or flighty, light-headed person.
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.
O.E. undon "to unfasten and open" (a window or door), "to unfasten by releasing from a fixed position," from un- (2) + do. Undone "not accomplished" is recorded from c.1300; sense of "destroyed" is recorded from mid-14c.; the notion is of "to annul something
that was done." Undoing "action of bringing to ruin" is recorded from late 14c.