The word is rare in Anglo-Norman (although not in Continental French), and could possibly be interpreted as a misreading for nunpurcant, and thus a variant of nunpurquant.
adv.
1nevertheless, all the same:
(
1354; MS: c.1360
)
jeo m'en passe si brief comme jeo puisse, pur aler a matire [...] Non pur tant (var. (C: s.xivex) Nepurquant), loons, mercions et rendons graces a Nostre Seignur
29
[nunpurtant] (1354)