WordNet sense 1 ((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):

multiplicative inverse

WordNet sense 2 (expressing a reciprocal or complementary relation):

correlative

WordNet sense 3 (concerning each of two or more persons or things; especially given or done in return):

mutual

WordNet sense 4 (hybridization involving a pair of crosses that reverse the sexes associated with each genotype):

reciprocal cross

WordNet sense 5 (opposite in nature or effect or relation to another quantity ):

inverse