reciprocal

(noun) something (a term or expression or concept) that has a reciprocal relation to something else. Example: "Risk is the reciprocal of safety."

(noun) (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. Synonyms: multiplicative inverse.

(noun) hybridization involving a pair of crosses that reverse the sexes associated with each genotype. Synonyms: reciprocal cross.

(adj) concerning each of two or more persons or things; especially given or done in return. Synonyms: reciprocal (vs. nonreciprocal), mutual. Examples: "Reciprocal aid." "Reciprocal trade." "Mutual respect." "Reciprocal privileges at other clubs."

(adj) of or relating to the multiplicative inverse of a quantity or function. Example: "The reciprocal ratio of a:b is b:a."