Late 16th century (as an adjective in the sense 'oblique'): from an Old French diminutive of baif 'open-mouthed', from baer 'to gape' (see bay³).

• bay from Middle English:

  Hounds have bayed since the Middle Ages. Like bark, the word probably imitates the sound. People can now also bay for blood, when they call loudly for someone to be punished. The related phrase at bay comes from hunting and means ‘cornered, forced to face one's attackers’. It is often used now in to hold someone at bay, ‘to prevent someone from approaching or having an effect’. The geographical bay (Late Middle English) can be traced back to Old French baie, from Old Spanish bahia, but no further. The bay tree (Late Middle English) came via Old French from Latin bāca ‘berry’, and the type of bay found in a bay window, also late Middle English, comes from Old French baie, from the verb baer ‘to gape’. This is also, via baif ‘open-mouthed’ the source of bevel (late 16th century). See also baize