mid-13c. (late 12c. as a surname), of animals, "ferocious;" c. 1300, "wild, undomesticated, untamed," also "wild, uncultivated" (of land or places), from Old French sauvage, salvage "wild, savage, untamed, strange, pagan," from Late Latin salvaticus, alteration (vowel assimilation) of silvaticus "wild, woodland," literally "of the woods," from silva "forest, grove" (see sylvan).
Of persons, "indomitable, valiant," also "fierce, bold, cruel" (c. 1300); from late 14c., of persons or behavior, "wild, barbarous, uncivilized;" c. 1400 as "reckless, ungovernable," and by 1610s as "pertaining to or characteristic of savage peoples, living in the lowest condition of development." In heraldry, "naked or clothed in foliage" (1570s). The -l- often was restored in 16c.-17c. English spelling.
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].