Something (a term or expression or concept) that has a reciprocal relation to something else

(mathematics) one of a pair of numbers whose product is 1: the reciprocal of 2/3 is 3/2; the multiplicative inverse of 7 is 1/7

Hybridization involving a pair of crosses that reverse the sexes associated with each genotype

A reciprocal construction is a grammatical pattern in which each of the participants occupies both the role of agent and patient with respect to the other.

The social norm of reciprocity is the expectation that people will respond to each other in similar ways—responding to gifts and kindnesses from others with similar benevolence of their own, and responding to harmful, hurtful acts from others with either indifference or some form of retaliation.

Concerning each of two or more persons or things; especially given or done in return

Of or relating to the multiplicative inverse of a quantity or function