Reciprocal

1. The quotient arising from dividing unity by any quantity; thus, / is the reciprocal of 4; 1/(a +b) is the reciprocal of a + b. The reciprocal of a fraction is the fraction inverted, or the denominator divided by the numerator.
2. Reflexive; -- applied to pronouns and verbs, but sometimes limited to such pronouns as express mutual action.
3. Done by each to the other; interchanging or interchanged; given and received; due from each to each; mutual; as, reciprocal love; reciprocal duties.
4. That which is reciprocal to another thing.
5. Used to denote different kinds of mutual relation; often with reference to the substitution of reciprocals for given quantities. See the Phrases below.
6. Mutually interchangeable.
7. Recurring in vicissitude; alternate.