brother

noun
a man or boy who has the same parents as you:
My younger brother is called Mark.
Gavin and Nick are brothers.
Have you got any brothers and sisters?

Longman Dictionary of Contemporary English

brother

I. broth‧er¹ S1 W1 /ˈbrʌðə $ -ər/ BrE AmE noun [countable]
[Word Family: noun: ↑brother, ↑brotherhood; adjective: ↑brotherly]
[Language: Old English; Origin: brothor]
1. a male who has the same parents as you ⇨ sister:
I have two brothers, William and Mark.
elder/older/younger etc brother
My younger brother is a doctor.
little/kid brother (=younger brother)
I have to take my little brother to school.
My big brother (=older brother) has always looked after me.
my twin brother
2. spoken informal a word meaning a black man, used especially by other black men
3. a male member of a group with the same interests, religion, profession etc as you
4. (plural brothers or brethren) a male member of a religious group, especially a ↑monk:
Brother Justin
5. American English a member of a ↑fraternity (=a club of male university students)
6. brothers in arms literary soldiers who have fought together in a war
⇨ ↑Big Brother, ↑blood brother, HALF BROTHER, ↑stepbrother
• • •
COLLOCATIONS
■ ADJECTIVES/NOUN + brother
▪ an older/elder brother I have two older brothers.
▪ a big brother (=older brother - used especially by or to children) Jake was my big brother and I admired him.
▪ a younger brother Do you have any younger brothers?
▪ a little brother (also a kid brother American English) (=younger brother) My kid brother was always annoying me.
▪ a baby brother (=brother who is still a baby) Mum let me hold my new baby brother.
▪ a twin brother Luke and his twin brother Sam went everywhere together.
▪ a half-brother (=brother with only one parent the same as yours) I never really liked my half-brother.
▪ a step-brother (=the son of your stepfather or stepmother) His dad’s new wife brought him two step-brothers.
II. brother² BrE AmE interjection especially American English
used to show you are annoyed or surprised:
Oh, brother – I really don’t want to deal with this now.

Oxford Advanced Learner's Dictionary

brother

brother [brother brothers brethren] noun, exclamation [ˈbrʌðə(r)] [ˈbrʌðər]

noun

IN FAMILY
1. a boy or man who has the same mother and father as another person
• We're brothers.
• He's my brother.
• an older/younger brother
• a twin brother
• Does she have any brothers and sisters?
• Edward was the youngest of the Kennedy brothers.
• He was like a brother to me (= very close).

see also half-brother, stepbrother

OTHER MEN

2. (pl. brothers or old-fashioned brethren)used for talking to or talking about other male members of an organization or other men who have the same ideas, purpose, etc. as yourself
• We must work together, brothers!
• We are all brothers in the fight against injustice.
• He was greatly respected by his brother officers.

• We must support our weaker brethren.

IN RELIGIOUS GROUP

3. (also Brother)(pl. brethren or brothers) a male member of a religious group, especially a monk
• Brother Luke

• The Brethren meet regularly for prayer.

FORM OF ADDRESS

4. (NAmE, informal) used by black people as a form of address for a black man

AT COLLEGE/UNIVERSITY
5. (in the US) a member of a fraternity (= a club for a group of male students at a college or university)
Word Origin:
Old English brōthor, of Germanic origin; related to Dutch broeder and German Bruder, from an Indo-European root shared by Latin frater.
Example Bank:
• Bill idolizes his big brother, who is a professional footballer.
• Do you have any brothers and sisters?
• He married the wife of his late brother.
• His old teacher greeted him like a long-lost brother.
• She wrote daily to her beloved brother, Leo.

• The boys are so close, they're like brothers.

exclamation (old-fashioned, especially NAmE) used to express the fact that you are annoyed or surprised
• Oh brother!
Word Origin:

Old English brōthor, of Germanic origin; related to Dutch broeder and German Bruder, from an Indo-European root shared by Latin frater.

Cambridge Advanced Learner's Dictionary

brother

brother /ˈbrʌð.əʳ/ US /-ɚ/
noun [C]
1 a man or boy with the same parents as another person:
Do you have any brothers and sisters?
I have three brothers and a sister.
Johnny is my younger/older/big/baby/little brother.
My brother lives in Washington.

2 a man who is a member of the same group as you or who shares an interest with you or has a similar way of thinking to you:
[as form of address] "Let us unite, brothers and fight this unjust law!"

3 used as the title of a man, such as a monk, who belongs to a religious organization:
Brother Michael and Brother John were deep in conversation.

4 US INFORMAL sometimes used by a black man to address or refer to another black man

brotherly /ˈbrʌð.^əl.i/ US /-ɚ.li/
adjective
showing the kindness, interest or affection that you would expect a brother to show:
Can I give you some brotherly advice?

Collins COBUILD Advanced Learner’s English Dictionary

brother

/brʌðə(r)/
(brothers)

Frequency: The word is one of the 700 most common words in English.

Note: The old-fashioned form 'brethren' is still sometimes used as the plural for meanings 2 and 3.

1.
Your brother is a boy or a man who has the same parents as you.
Oh, so you’re Peter’s younger brother...
Have you got any brothers and sisters?
N-COUNT: oft poss N
see also half-brother, stepbrother

2.
You can describe a man as your brother if he belongs to the same race, religion, country, profession, or trade union as you, or if he has similar ideas to you.
He told reporters he’d come to be with his Latvian brothers.
N-COUNT: usu poss N

3.
Brother is a title given to a man who belongs to a religious community such as a monastery.
...Brother Otto.
...the Christian Brothers community which owns the castle.
N-TITLE; N-COUNT; N-VOC

4.
Brothers is used in the names of some companies and shops.
...the film company Warner Brothers...
N-IN-NAMES

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

brother

broth·er /ˈbrʌðɚ/ noun, pl -ers [count]
1 : a boy or man who has one or both of the same parents as you
• my little/younger brother
• her big/older brother
• Her brother was adopted.
- compare brother-in-law, half brother, stepbrother
2 : a man who is from the same group or country as you
• his college fraternity brothers
• We must support our brothers and sisters fighting overseas.
3 pl broth·ers or breth·ren /ˈbrɛðrən/ : a male member of a religious group
• the brothers in a monastery
- used especially as a title
• Brother John
4 US informal : a black man - used especially by African-Americans;
5 US informal
- used when talking to a man
• Brother, do you have an extra cigarette?
• Brother, you have got to relax.
6 chiefly US informal
- used as an interjection to express surprise or annoyance
• Brother was I ever sick. [=I was very sick]
• Oh, brother!