LSJ
gen. -εω, τό, half-ἑκτεύς, acc. sg. -εων (written -εον) ib. 12.76.7; gen. -εω ib. 22.1356; but -έου Ar. Nu. 643; nom. -έον ib. 645, Mémoires présentés à l΄Acad. des Inscr. 1923.2 (iv BC); written -ειον ibid. ; pl. -εια IG2². 1672.15, 268, al. ; ἡμιεκτέα prob. cj. in Pl.Com. 174.12; Ion. pl. -εκτῆ Milet. 7.27. (Accent doubtful, parox. in codd. ; -ειον, εια may have short ει as in εἰάν, etc.)
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)