Unctuous comes from Medieval Latin unctuosus ('greasy'), from Latin unctus ('anointed, oiled'), past participle of unguere ('to anoint, smear with oil'). The historical chain includes Latin unctuosus, Latin unguere, and Proto-Indo-European *h₃engʷ-. The quoted older senses, "greasy", "anointed, oiled", and "to anoint, smear with oil", supply the semantic anchors for unctuous. The formation is best read as participial and borrowed: the word unctuous carries its older form-history into a compact English lexical shape. In present English it is used as a adj, "excessively flattering or ingratiating; oily". English derivatives include unctuously and unctuousness; related English forms include unction, unguent, and anoint. The result is a adj whose etymology preserves both the older form and the later English specialization.