The headword is the imperfect indicative middle/passive, third person plural, of the verb oi)/gnumi: LSJ entry at web address 1. The gloss is the corresponding form of the compound -- and far commoner -- verb a)noi/gnumi (in its thematic variant a)noi/gw). From the scholia to Homer, Iliad 2.809 [web address 2] (cf. 8.58), where the headword occurs (of gates). Same or similar glosses in Photius and other lexica. See also omega 38, where the uncontracted form is listed; also other forms of this verb at omicroniota 21 and omega 39.