Bailly
(ὁ) seul. acc. ῦν, t. enfantin, papa, THCR. Idyl. 15, 15.
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LSJ
(for the accent cf. Hdn. Gr. 2.936), gen. ύος, ὁ, a term of endearment used by children to their father, papa, Theoc. 15.14; — Eust. (v. v.) expld. as ὁ ἀφ’ οὗ ἔφυ.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)