Present participle, masculine nominative singular, of the epic/poetic verb λιγαίνω (only in present and imperfect); see generally Homer, Iliad 11.685 (web address 1). Perhaps quoted here from Apollonius Rhodius, Argonautica 1.740.
The word is glossed as κηρύσσων in Photius and as μέλπων, ἡδεως ὑμνῶν in Hesychius; cf. Hesychius s.v. λιγαίνει and λίγαινον and Etymologicum magnum s.v. λίγεια .