ice-cube n.

Old English is "ice, piece of ice" (also the name of the Anglo-Saxon rune for -i-), from Proto-Germanic *is- "ice" (source also of Old Norse iss, Old Frisian is, Dutch ijs, German Eis), of uncertain origin; possible relatives are Avestan aexa- "frost, ice," isu- "frosty, icy;" Afghan asai "frost." Slang meaning "diamonds" is attested from 1906.

Modern spelling begins to appear 15c. and makes the word look French. On ice "kept out of the way until wanted" is from 1890. Thin ice in the figurative sense is from 1884. To break the ice "to make the first opening to any attempt" is from 1580s, metaphoric of making passages for boats by breaking up river ice though in modern use it usually has implications of "cold reserve." Ice-fishing is from 1869; ice-scraper is from 1789 in cookery.

1550s, "regular geometric body with six square faces," also "product obtained by multiplying the square of a quantity by the quantity itself," from French cube (13c.) and directly from Latin cubus, from Greek kybos "a six-sided die," used metaphorically of dice-like blocks of any sort, also "cake; piece of salted fish; vertebra," of uncertain origin. Beekes points out that "words for dice are often loans" and that "the Lydians claimed to have invented the game" of kybos.

The mathematical also was in the ancient Greek word: the Greeks threw with three dice; the highest possible roll was three sixes. The word was attested in English from late 14c. in Latin form. The 1960s slang sense of "extremely conventional person" (1959) is from the notion of a square squared. Cube-root is from 1550s (in Middle English this was simply a cubick).