The word is attested only once in Anglo-Norman, and although a plausible creation, it may be considered a corruption of afuster: 'to put into position' (cf. the reflexive use in Rom de Rouwace, also with reference to archers).
v.n.
1to group together:
(
s.xii3/3; MS: s.xiiim
)during the hunt for a stag: Li reis ad sa gent ordinee Et feit afuscher ses archers, Ses fols chens feit cure premers, Set vinz en leist aler ensemble; Trestut le bois tentist e tremble
1845