A respelling of base under the influence of Italian basso.
From Middle English bace, bas, alteration of bars, from Old English bærs ("a fish, perch"), from Proto-West Germanic *bars, from Proto-Germanic *barsaz ("perch"), from Proto-Indo-European *bʰórsos ("prickle, thorn, scale"). Cognate with Dutch baars ("perch, bass"), German Barsch ("perch"). More at barse.