Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
relation, relative (nn.)
These are synonyms that mean “someone to whom I am related, by blood, marriage, or some other link to be specified.” There’s no difference between She’s a close relative and She’s a close relation. Generally when a family relationship is to be specified or denied, the preposition to be used is of—She’s a relative [relation] of mine—but sometimes you may encounter the preposition to, especially in the negative: She’s no relation to me. In structures like the last, relative and relation are not quite fully interchangeable in Standard English.
