1) In the wall frame of a timber building a bay is the space between two sets of principal posts, so a three-bay house has two end walls and two pairs of intermediate posts. Local building practices meant that ‘bay’ came to be considered as a standard width although it differed from region to region.
1579 a measse of Fyve bayes, Sheffield
1587 the lathe conteyninge two bayes and one outshutt, Thurstonland
1630 foure bayes of howseinge in Honley
1733-4 one bay in the west end of the Brick Laith, Pudsey.
2) A fabric with worsted warp and woollen weft introduced into England in the sixteenth century, notably into Essex (FAW69).
It was referred to in an Act of 1581 as ‘bays’ and there was a large output in Yorkshire by the next century: 1655 my red bayes gowne, Babthorpe. The OED says under ‘baize’ that the plural form of the adopted word was misunderstood, and treated as a collective singular, occasionally with ‘bayses’ as a plural: 1656 Item eleaven blacke baizes att nine shillings per peece, Eshton
1706 Our Bayes market for the heavier sorts very brisk, Halifax
1730 illegally worked six cloths or Bazes, Sowerby.
3) An embankment or dam to retain water.
c.1590 The milln for wheles bayes water workes and roofe xx okes, North Newbald
1612-6 all the tymber that shalbe needfull for ground workes for 2 wheles and fouer stockes ... and plankes for the whole baye, Huddersfield.