1620s "cause to lose flesh" (implied in emaciating), from Latin emaciatus, past participle of emaciare "make lean, cause to waste away," from assimilated form of ex- "out" (see ex-) + macies "leanness," from macer "thin" (see macro-). Intransitive meaning "become lean, waste away" is from 1640s. Related: Emaciated.