reciprocal

The number obtained by dividing 1 by another given number; the result of exchanging the numerator and the denominator of a fraction.

“0.5 is the reciprocal of 2.”

(grammar) A construction expressing mutual action.

Of a feeling, action or such: mutual, uniformly felt or done by each party towards the other or others; two-way.

“reciprocal love; reciprocal duties”

Mutually interchangeable.

(grammar) expressing mutual action, applied to pronouns and verbs; also in a broad sense: reflexive

Used to denote different kinds of mutual relation; often with reference to the substitution of reciprocals for given quantities.

Done, given, felt, or owed in return

“a reciprocal invitation to lunch”