"very hard mineral" (crystalline aluminum oxide) used for grinding and polishing other gems, steel, etc., 1728, from Anglo-Indian, from Tamil (Dravidian) kurundam "ruby sapphire" (Sanskrit kuruvinda), which is of unknown origin. It is a dull or opaque variety of sapphire, amethyst, ruby, and topaz; in hardness it is next to diamond.
Used in ancient Greece of a blue gem, perhaps sapphire, and of a purple or deep red flower, but exactly which one is unknown (gladiolus, iris, and larkspur have been suggested). It is fabled to have sprung from the blood of Hyakinthos, Laconian youth beloved by Apollo and accidentally slain by him. The flower is said to have the letters "AI" or "AIAI" (Greek cry of grief) on its petals. The modern use in reference to a particular flowering plant genus is from 1570s. Related: Hyacinthine.
It is perhaps literally "invincible, indomitable," from a- "not" (see a- (3)) + daman "to conquer, to tame," from PIE root *deme- "to constrain, force, break (horses)" (see tame (adj.)). "But semantically, the etymology is rather strange," according to Beekes, who suggests it might be a foreign word altered in Greek by folk etymology, and compares Akkadian (Semitic) adamu.
Applied in antiquity to a metal resembling gold (Plato), white sapphire (Pliny), magnet (Ovid, perhaps through confusion with Latin adamare "to love passionately"), steel, emery stone, and especially diamond, which is a variant of this word. "The name has thus always been of indefinite and fluctuating sense" [Century Dictionary].