(chiefly US, colloquial, idiomatic, somewhat vulgar) To be manly, brave.

(set theory) An object containing exactly two elements in a fixed order, so that, when the elements are different, exchanging them gives a different object. Notation: (a, b) or ⟨a,b⟩.

(cricket) The score of zero runs, having been out on the first ball faced in each innings of a two-innings match; a golden duck in each innings

A single girl (or, rarely, a boy), usually a foreigner, who helps a host family with childcare, housework, or both while staying as a guest with a host family, and generally receives a small allowance (or pocket money).

(geometry) The two supplementary adjacent angles formed by two intersecting lines

(chemistry) A pair of electrons in the valence shell of an atom that does not participate in bonding.

(phonology) A pair of words differing by only one phonetic segment or suprasegment, used to prove the validity of a proposed phoneme, toneme, or chroneme.

plural of minimal pair

A relationship, often permanent, formed between a male and female animal; initiated during courtship and maintained after mating.

(physics) A pair of electrons (or other fermions), of opposite spin, whose theorised behaviour is the basis of the BCS theory of superconductivity.