Two chromosomes that are identical, with the same genes.

(biology) In molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds.

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

(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⟩.

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

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

(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.

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

An item of clothing that is worn under one's trousers or pants.