From Liddell and Scott Greek-English lexicon, on ἀδελφός
ἀδελφός [ᾰ] , ( ἀ - copul., δελφύς, Arist. HA 510b13 ; cf. ἀγάστωρ ) properly, son of the same mother : I as Subst. , ἀδελφός, ὁ , voc. ἄδελφε; Ep. , Ion. , and Lyr. ἀδελφεός (gen. -ειοῦ in Hom. is for -εόο ), Cret. ἀδελφιός, ἀδευφιός, Leg.Gort. 2.21, Mon.Ant. 18.319: — brother , Hom. , etc.; ἀδελφοί brother and sister , E. El. 536 ; so of the Ptolemies, θεοὶ ἀδελφοί Herod. 1.30 , OGI 50.2 (iii B. C.) , etc.; ἀπ' ἀμφοτέρων ἀδελφεός Hdt. 7.97 : prov., χαλεποὶ πόλεμοι ἀδελφῶν E. Fr. 975 : metaph., ἀ. γέγονα σειρήνων LXX Jb. 30.29 .
2. kinsman , ib. Ge. 13.8 , al.; tribesman, Ex. 2.11 , al.
3. colleague, associate, PTeb. 1.12, IG 12 (9).906.19 ( Chalcis ); member of a college , ib.14.956.
4. term of address, used by kings, OGI 138.3 ( Philae ), J. AJ 13.2.2 , etc.; generally, LXX Ju. 7.30 ; esp. in letters, PPar. 48 (ii B. C.) , etc.: — as a term of affection, applicable by wife to husband, LXX To. 10.12 , PLond. 1.42.1 (ii B. C.) , etc.
5. brother (as a fellow Christian), Ev.Matt. 12.50 , Act.Ap. 9.30 , al.; of other religious communities, e.g. Serapeum, PPar. 42.1 (ii B. C.) , cf. PTaur. 1.1.20 .
6. metaph., of things, fellow , ἀνὴρ τῷ ἀ. προσκολληθήσεται, of Leviathan's scales, LXX Jb. 41.8 . II Adj. , ἀδελφός, ή , όν , brotherly or sisterly , A. Th. 811 , etc.; φύσιν ἀ. ἔχοντες, of Hephaistos and Athena, Pl. Criti. 109c .
2. generally, of anything double, twin, in pairs , X. Mem. 2.3.19 : — also, akin, cognate, μαθήματα Archyt. 1 ; ἀ. νόμοις Pl. Lg. 683a : mostly c. gen., ἀδελφὰ τῶνδε S. Ant. 192 ; ἡ δὲ μωρία μάλιστ' ἀ. τῆς πονηρίας ἔφυ Id. Fr. 925 ; freq. in Pl. , Phd. 108b , Cra. 418e , al., cf. Hyp. Epit. 35 : c. dat., ἀδελφὰ τούτοισι S. OC 1262 , cf. Pl. Smp. 210b .