reciprocal - noun

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

reciprocal - adjective

• 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

reciprocal - thesaurus

mutual