plural of die (n.), early 14c., des, dys, plural of dy, altered 14c. to dyse, dyce, and 15c. to dice. "As in pence, the plural s retains its original breath sound, probably because these words were not felt as ordinary plurals, but as collective words" [OED]. Sometimes used as singular 1400-1700. Dice-box "box from which dice are thrown in gaming" is from 1550s.
late 14c., "to cut into cubes," from dice (n.). Meaning "to play at dice" is from early 15c. Related: Diced; dicing.