Acetous (#; 277), a.
Etymology: [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.
Shades of meaning
Fernald has no entry of its own for acetous; he lists it under bitter.
He lists it without comment; the entries above explain its neighbors.