uncurl (v.)

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)).

late 14c. (implied in curled), "turn, bend, form in ringlets" (transitive), a metathesized formation corresponding to the Middle English adjective crull, crulle (c. 1300), which is probably from an unrecorded Old English word or from Middle Dutch krul "curly," from Proto-Germanic *krusl- (source also of East Frisian krull "lock of hair," Middle High German krol, Norwegian krull, Danish krølle "curl").

Intransitive sense of "take the form of a curl, assume a spiral shape" is from 1520s (originally of hair). Meaning "to play at curling" is from 1715.  Related: Curled; curling.