= y not, I do not know: see NOT v.2
1297. R. Glouc. (Rolls), 5628. Þere he liþ ȝut to þis day ac ynot to wuche dome Þe toun suþþe of pokel chirche fram glastingbury come.
13[?]. in Ritson, Anc. Songs (1877), 57. Ynot non so freoh flour, Ase ledies that beth bryght in bour.
