probably a nursery or jocular word, imitating the action of the lips in an infant's kiss; but cf. Old French baer, beer, to open the mouth, gape;
or, a contracted form of basse to kiss
From: The British Poets, Including Translations
The Poems of Geoffrey Chaucer, Volume I
Printed by C. Whittingham, 1822
Canterbury Tales. The Wif of Bathes Prologue.