for the verb: probably a nursery or jocular word, imitating the action of the lips in an infant’s kiss;
Old French has baer, beer (to open the mouth, to gape);
also, possibly a contracted form of basse (to kiss)
EXAMPLE (for verb)
“…Thanne wolde I seye, “Goode lief, taak keep
How meekly looketh Wilkyn, oure sheep!
Com neer, my spouse, let me ba thy cheke!
Ye sholde been al pacient and meeke…”
From: The Wife of Bath’s Prologue
By Geoffrey Chaucer, c1386