reciprocal

Etymology

Latin reciprocus, possibly from a phrase such as reque proque (“back and forth, to and fro”), from re- (“back”), prō (“forwards”) and -que (“and”).

adj

1. 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
2. Mutually interchangeable.
3. (grammar) Expressing mutual action, applied to pronouns and verbs; also in a broad sense: reflexive.
4. (mathematics) Used to denote different kinds of mutual relation; often with reference to the substitution of reciprocals for given quantities.
5. Done, given, felt, or owed in return.
   a reciprocal invitation to lunch

noun

1. (arithmetic) 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.
2. (grammar) A construction expressing mutual action.
   Depending on where reciprocalization applies (syntax vs. lexicon), the relevant reciprocal verbs are claimed to exhibit specific properties, in particular: (i) syntactic reciprocals are fully productive whereas lexical reciprocals have only limited productivity; […] 2008, Ekkehard König, Volker Gast, Reciprocals and Reflexives: Theoretical and Typological Explorations