Acetous \A*ce"tous\ (#; 277), a. [L. acetum vinegar, fr. acere to be sour.] 1. Having a sour taste; sour; acid. ``An acetous spirit.'' --Boyle. ``A liquid of an acetous kind.'' --Bp. Lowth. 2. Causing, or connected with, acetification; as, acetous fermentation. {Acetous acid}, a name formerly given to vinegar