The context is not specific enough to determine the exact meaning of this word, apparently not attested elsewhere. The association with pinna is conjectural, and the lexeme may instead be a derivative of pannus (see pan1).
s.
1pennon, banner, long and narrow flag (usually attached to a lance) (?):
(
1339
)
Item, qe les espringalx, engyns, arblastes, actines, lances, payneys, blasouns, targes, purkernels [...] soient liverez au dit gardeyn
ii 108.22
[peneis] (1339)