The term fra/thr (Ionic frh/thr) is the Greek cognate of Latin frater, Sanskrit bhrātar-, English "brother," etc., but was used to designate a member of a larger kinship group, the "brotherhood" (fra/tra or fratri/a). In the various dialects, the second rho is often dropped by dissimilation. *fra/twr is a later (according to Herodian) variant of fra/thr with a different vowel-grade, perhaps extracted from compounds like a)fra/twr/a)frh/twr. See Chantraine s.v. fra/thr for fuller discussion.
See also phi 693, and cf. phi 136, phi 281, phi 711, gamma 146, gamma 147.
[1] Likewise in Lexica Segueriana 313.27-31, and cf. a scholion on Plato, Timaeus 21B.
[2] Entry so far = Photius, Lexicon phi290 Theodoridis. The source of this final sentence, additional to what is found elsewhere (see preceding note), is unidentifiable. The word 'race' is textually shaky; the mss vary between e)/qnos and e)/qos; but Theodoridis declares e)/qnos correct, citing Pollux 8.111.
[3] Homer, Iliad 13.354 (web address 1).
[4] cf. a scholion on Aristophanes, Knights 255 (web address 2). *pa/trh, patria/ and pa/trios come from path/r "father," but in some dialects may be confused with forms from fra/thr (see LSJ s.v. fra/tra).
[5] cf. a scholion on Aristophanes, Birds 1669 (web address 3).