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.
1774, "glacier humped like a hill;" 1820 as "detached piece of a glacier or ice pack at sea," partial loan-translation of Dutch ijsberg, literally "ice mountain," from ijs "ice" (see ice (n.)) + berg "mountain" (from PIE root *bhergh- (2) "high," with derivatives referring to hills and hill-forts.). Similar formation in Norwegian isberg, Danish isbjerg.
Earlier English terms were sea-hill (1690s), island of ice (1610s). Phrase tip of the iceberg in a figurative sense (in allusion to most of it being unseen underwater) first recorded 1962. Iceberg lettuce attested from 1893, apparently originally a trade name.