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. [ 1913 Webster ]

2. Causing, or connected with, acetification; as, acetous fermentation. [ 1913 Webster ]

Acetous acid, a name formerly given to vinegar, which is a dilute solution of acetic acid. [ 1913 Webster +PJC ]