reciprocal vs synonymous

reciprocal

adj
  • Mutually interchangeable. 

  • Expressing mutual action, applied to pronouns and verbs; also in a broad sense: reflexive. 

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

  • Done, given, felt, or owed in return 

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

noun
  • A construction expressing mutual action. 

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

synonymous

adj
  • Having an identical meaning. 

  • Having a similar meaning. 

  • Such that both its forms yield the same sequenced protein. 

  • Of, or being a synonym. 

How often have the words reciprocal and synonymous occurred in a corpus of books? (source: Google Ngram Viewer )