adj. & n.
adj. 1 in return (offered a reciprocal greeting). 2 mutual (their feelings are reciprocal). 3 Gram. (of a pronoun) expressing mutual action or relation (as in each other). 4 inversely correspondent; complementary (natural kindness matched by a reciprocal severity).
n. Math. an expression or function so related to another that their product is unity (« is the reciprocal of 2). reciprocality n. reciprocally adv.
[ L reciprocus ult. f. re- back + pro forward ]