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.
It forms all or part of: barrow (n.2) "mound, hill, grave-mound;" belfry; borough; bourgeoisie; burg; burgess; burgher; burglar; faubourg; iceberg.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit b'rhant "high," brmhati "strengthens, elevates;" Avestan brzant- "high," Old Persian bard- "be high;" Greek Pergamos, name of the citadel of Troy; Old Church Slavonic bregu "mountain, height;" Old Irish brigh "mountain;" Welsh bera "stack, pyramid."