Ethereous \E*the"re*ous\, a. [L. aethereus, Gr. ? See {Ether}.] 1. Formed of ether; ethereal. [Obs.] This ethereous mold whereon we stand. --Milton. 2. (Chem.) Pertaining to, or resembling, ether. {Ethereous oil}. See {Ethereal oil}, under {Ethereal}.