Definition of "Reciprocal" :

noun: hybridization involving a pair of crosses that reverse the sexes associated with each genotype

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

noun: something (a term or expression or concept) that has an inverse relation to something else

"Risk is the reciprocal of safety."

adjective: of or relating to the multiplicative inverse of a quantity or function

"The reciprocal ratio of a:b is b:a."

adjective: concerning each of two or more persons or things; especially given or done in return

"Reciprocal aid."