amalgam (n.)
c. 1400, "a blend of mercury with another metal; soft mass formed by chemical manipulation," from Old French amalgame or directly from Medieval Latin amalgama, "alloy of mercury (especially with gold or silver)," an alchemists' word of uncertain origin.

Perhaps an alteration of Latin malagma "poultice, plaster," probably from Arabic al-malgham "an emollient poultice or unguent for sores (especially warm)" [Francis Johnson, "A Dictionary of Persian, Arabic, and English"], perhaps from Greek malagma "softening substance," from malassein "to soften," from malakos "soft" (from PIE *meldh-, from from root *mel- (1) "soft"). Figurative meaning "compound of different things" is from 1790.