brother

UK: /ˈbrʌðə^r/ US: /ˈbrʌðɚ/ ,(bruᵺ′ər or, for 9, bruᵺ′ûr′)

Inflections of 'brother' (n):

brothers

npl (All usages)

brethren

npl (Archaic except for senses relating to religious orders or fellowship)

WordReference Random House Learner's Dictionary of American English © 2025

broth•er /ˈbrʌðɚ/   n., pl. broth•ers, (Archaic) breth•ren /ˈbrɛðrən/ ;
interj. 
n. [countable]

1. a male relative who has the same parents as another:
   She had only one brother.
2. a man or person in the same group, nationality, etc., as another:
   We should remember that all these people are our brothers.
3. Religion [often: Brother] a man who devotes himself to the duties of a religious order without taking holy orders.
4. Slang Terms Slang. fellow;
   buddy:
   Brother, can you spare a dime?

interj. 

5. Slang Terms (used to show disappointment, disgust, or surprise):
   Oh, brother! I forgot my tickets.

WordReference Random House Unabridged Dictionary of American English © 2025

broth•er  (bruᵺ′ər or, for 9, bruᵺ′ûr′), n., pl. brothers, (Archaic) brethren;
 interj. 
n. 

1. a male offspring having both parents in common with another offspring;
   a male sibling.
2. Also called half brother. a male offspring having only one parent in common with another offspring.
3. a stepbrother.
4. a male numbered among the same kinship group, nationality, race, profession, etc., as another;
   an associate;
   a fellow member, fellow countryman, fellow man, etc.:
   a fraternity brother.
5. [Eccles.]
   • (often cap.) a male numbered among the lay members of a religious organization that has a priesthood.
   • a man who devotes himself to the duties of a religious order without taking holy orders, or while preparing for holy orders.
6. brothers, all members of a particular race, or of the human race in general:
   All men are brothers.
7. Slang Terms fellow;
   buddy:
   Brother, can you spare a dime?
8. Informal Terms a black man;
   soul brother.

interj. 

9. Slang Terms (used to express disappointment, disgust, or surprise).

• bef. 1000; Middle English; Old English brōthor; cognate with Dutch broeder, German Bruder, Old Norse brōthir, Gothic brothar, Sanskrit bhrātṛ, Greek phrá̄tēr, Latin frāter, Old Irish bráthair, Old Church Slavonic bratrù

broth′er•less, adj. 
broth′er•like′, adj. 
Synonyms

• 1. Brothers, brethren are plurals of brother. Brothers are kinsmen, sons of the same parents:
  My mother lives with my brothers.
  Brethren, now archaic in the foregoing sense, is used of male members of a congregation or of a fraternal organization:
  The brethren will meet at the church.

Collins Concise English Dictionary © HarperCollins Publishers::

brother / ˈbrʌðə/ noun (brothers, (archaic except when referring to fellow members of a religion, sect, society, etc) brethren)

1. a male person having the same parents as another person
2. short for half-brother, stepbrother
3. a male person belonging to the same group, profession, nationality, trade union, etc, as another or others; fellow member
4. (as modifier): brother workers
5. comrade; friend: used as a form of address
6. a member of a male religious order who undertakes work for the order without actually being in holy orders
Related adjective(s): fraternal

Etymology: Old English brōthor; related to Old Norse brōthir, Old High German bruoder, Latin frāter, Greek phratēr, Sanskrit bhrātar