The word is presumably an error for pos[i]sioun (see posicion), rather than an otherwise unattested derivative of pausare (see poser).
s.
1lawsupposition, postulation of a hypothetical case:
(
1329-30
)
Nous trovoms qe mesme la possioun et mesme la demande furent al dereyn eyer qe fust avaunt només. Al quele vous respondistis come ore avetz respondu
3-4 Ed III 21
(possioun) (1329-30)