"two times, on two occasions, in two instances," late Old English twies, from Old English twiga, twigea "two times," from Proto-Germanic *twiyes (source also of Old Frisian twia, Old Saxon tuuio), from PIE *dwis-, adverbial form of root *dwo- "two." Spelling with -ce reflects the voiceless pronunciation.

Life is as tedious as a twice-told tale

Vexing the dull ear of a drowsy man.

["King John," III.iv.]

Think twice, then speak was an "old Prouerbe" by 1623. At twice, though less common than at once, means "at two distinct times; by two distinct operations."

"cloth woven in parallel diagonal lines," early 14c., Scottish and northern English variant of Middle English twile, from Old English twili "woven with double thread, twilled," partial loan-translation of Latin bilix "with a double thread" (with Old English twi- substituted for cognate Latin bi-, both from PIE root *dwo- "two"); the second element from Latin licium "thread," a word of unknown etymology.