Obsolete form of reciprocal.

plural of reciprocity

(biology) The phenomenon of two organisms acting in ways that mutually benefit one another.

(grammar) A pronoun referring to an antecedent in the plural, and expressing a mutual relation.

plural of reciprocal pronoun

(mathematics) Synonym of inverse proportion

plural of reciprocal altruism

(ethics) The golden rule used by philosophers.

(number theory) The mathematical theorem which states that, for given odd prime numbers p and q, the question of whether p is a square modulo q is equivalent to the question of whether q is a square modulo p.

A piston engine.