The half brother of one's spouse. / The husband of one's half-sibling. / The husband of the half-sibling of one's spouse.

(uncommon) One's spouse's brother-in-law (one's spouse's sibling's husband), especially one's wife's sister's husband; either of two (or more) men who marry sisters, in relation to the other; the brother of one spouse in relation to the siblings of the other spouse.

(idiomatic) A large number of people; most people.

Alternative spelling of three-quarter brother

(horse breeding) The male offspring of a horse's sire/dam that is by/out of a sibling of its other parent. / (horse breeding) The male offspring of a horse's dam and a son of its sire.

The brother of one's boyfriend or girlfriend. / Boyfriend of one's sister or brother. / The brother of one's ex-spouse.

Alternative form of everyone and his brother

Used to ask whether someone has any siblings.

(informal) A very close male friend.

(humorous, rare) Bob's your uncle