Origin and history of uncap

c. 1400, "to put a cap on," from cap (n.); the meaning "cover as with a cap" is from c. 1600. The figurative sense of "complete, consummate, bring to a climax" is from 1580s; that of "go one better, outdo, excel" is by 1821. Related: Capped; capping. To cap verses (1610s) was "to quote alternately verses each beginning with the same letter with which the last ended."

The capping of Latin verses is a common game in classical schools. No verse may be used twice, and no hesitation or delay is permitted; so that a moderate proficiency in the game supposes several thousand verses arranged in the memory alphabetically. [Century Dictionary, 1895]

prefix of reversal, deprivation, or removal (as in unhand, undo, unbutton), Old English on-, un-, from Proto-Germanic *andi- (source also of Old Saxon ant-, Old Norse and-, Dutch ont-, Old High German ant-, German ent-, Gothic and- "against"), from PIE *anti "facing opposite, near, in front of, before, against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before").

More or less confused with un- (1) through similarity in the notions of "negation" and "reversal;" an adjective such as unlocked might represent "not locked" (un- (1)) or the past tense of unlock (un- (2)).