Abbott-Smith Manual Greek Lexicon
ἀδελφός (G80)
343 ἀδελφός , -οῦ, ὁ ( ἀ- copul., δελφύς , womb ), in cl., a brother , born of the same parent or parents. [In LXX (Hort, Ja. , 102 f.), for אָח ;] lit. of a brother ( Ge 4:2 , al.). Of a neighbour ( Le 19:17 ). Of a member of the same nation ( Ex 2:14 , De 15:3 ). In NT in each of these senses (1. Mt 1:2 , al.; 2. Mt 7:3 ; 3. Ro 9:3 ) and also, of a fellow-Christian: I Co 1:1 , Ac 9:30 . This usage finds illustration in π. , where ἀ. is used of members of a pagan religious community (M, Th. , I, 1:4; MM, VGT , s.v.). The ἀδελφοὶ τ. Κυρίου ( Mt 12:46-49 13:55 28:10 , Mk 3:31-34 , Lk 8:19-21 , Jo 2:12 7:3 , 5 10 20:17 , Ac 1:14 , I Co 9:5 ) may have been sons of Joseph and Mary (Mayor, Ja. , Intr. viff.; DB , i, 320 ff.) or of Joseph by a former marriage (Lft., Gal. , 252ff.; DCG , i, 232 ff.), but the view of Jerome, which makes ἀ. equivalent to ἀνεψιός , is inconsistent with Greek usage. (Cremer, 66.)
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain