broth·er / ˈbrə[voicedth]ər/ • n. 1. a man or boy in relation to other sons and daughters of his parents. ∎  a half-brother, stepbrother, or foster brother. ∎  a brother-in-law. ∎  a male associate or fellow member of an organization: fraternity brothers. ∎  inf. a black man (chiefly used as a term of address among black people). ∎  a fellow human being. ∎  a thing that resembles or is connected to another thing: the machine is almost identical to its larger brother.2. (pl. also breth·ren / ˈbre[voicedth]rin/ ) Christian Church a (male) fellow Christian. ∎  a member of a religious order or congregation of men: a Benedictine brother.• interj. used to express annoyance or surprise.DERIVATIVES: broth·er·li·ness n.broth·er·ly adj.ORIGIN: Old English brōthor, of Germanic origin; related to Dutch broeder and German Bruder, from an Indo-European root shared by Latin frater.

brother am I my brother's keeper? an expression of rejection for natural ties; originally a biblical quotation, from the response of Cain to God when asked the whereabouts of the murdered Abel (Geneis 4:9).
Brother Jonathan America personified. Recorded from the early 19th century, the term is said to come from the name applied to Jonathan Trumbull, Governor of New York, by George Washington, and to have been used originally with biblical reference to 2 Samuel 1:26.

See also Big Brother at big.

brother OE. brōðor, OS. brōðar, OHG. bruodar (G. bruder), ON. bróðir, Goth. brōpar :- Gmc. *brōþar :- IE. *bhrāter, whence Skr. bhrātr, Gr. phrātēr, L. frāter, OSl. bratrū, OCelt. *brāter (Ir., Gael. brathair, W. brawd, Breton breur).