The headword is a feminine noun in the nominative singular; see generally LSJ s.v.
Although this exact form of the headword is attested only here, the entry has probably been generated from instances of its oblique cases in Aristotle. See e.g. the dative singular at De caelo 297b13, where Aristotle explains that earth masses of any size will continue moving until they hold uniformly about a center, a)nisazome/nwn tw=n e)latto/nwn u(po\ tw=n meizo/nwn th=| prow/sei th=s r(oph=s, 'the lesser ones being forced to equalize themselves by the greater due to the forward drive of the impulse'. Note also two instances of the accusative case in the De mundo (396a8 & 20), in a passage of Posidonius reproduced in turn by Stobaeus.
[1] The gloss is the same form as the headword; cf. cognates at omega 41, pi 1236 (gloss), alpha 3676 (gloss), and see generally LSJ s.v.