See reciprocal in Webster's New World College Dictionary
adjective
done, felt, given, etc. in return: hoping for a reciprocal favor
present or existing on both sides; each to the other; mutual: to feel a reciprocal affection
corresponding but reversed or inverted
equivalent or interchangeable; corresponding or complementary
Gram. expressing mutual action or relation: “each other” is traditionally called a reciprocal pronoun
Math. of the reciprocals of quantities, or their relations
noun
anything that has a reciprocal action on or relation to another; complement, counterpart, equivalent, etc.
Math. the quantity resulting from the division of 1 by the given quantity; quantity which multiplied by the given quantity equals 1 (Ex.: the reciprocal of 7 is , of is 7)
Interchanged, given, or owed to each other: reciprocal agreements to abolish customs duties; a reciprocal invitation to lunch.
Performed, experienced, or felt by both sides: reciprocal respect.
Interchangeable; complementary: reciprocal electric outlets.
Grammar Expressing mutual action or relationship. Used of some verbs and compound pronouns.
Mathematics Of or relating to the reciprocal of a quantity.
Physiology Of or relating to a neuromuscular phenomenon in which the excitation of one group of muscles is accompanied by the inhibition of another.
Genetics Of or designating a pair of crosses in which the male or female parent in one cross is of the same genotype or phenotype as the complementary female or male parent in the other cross.
noun
Something that is reciprocal to something else.
Mathematics A number related to another in such a way that when multiplied together their product is 1. For example, the reciprocal of 7 is 1/7 ; the reciprocal of 2/3 is 3/2 .