The headword is third person singular, present indicative middle/passive, of the epic/poetic verb ἄγνυμι . Evidently quoted from somewhere -- perhaps Euripides, Helen 410 (web address 1).
[1] Same glossing in other lexica.
[2] Third person dual active, "broke through"; doubtless quoted from Homer, Iliad 12.148 (web address 2).
[3] Feminine genitive plural passive participle; instances in Homer, Iliad 16.769, Odyssey 10.123 (see web addresses 3 & 4).