αὐτάδελφος

η, ον, Subst., ἡ
A. brother's or sister's, αἷμα A. Th. 718, Eu. 89; αὐ. Ἰσμήνης κάρα S. Ant. 1.
II. Subst., one's own brother or sister, ib.503,696:—later αὐτ‐αδέλφη, ἡ, Sch.E. Ph. 135.
Liddell, Scott & Jones
A Greek-English Lexicon, 1940
An open-access project