WordNet sense 1 (a person related by blood or marriage):

relation

WordNet sense 2 (an animal or plant that bears a relationship to another (as related by common descent or by membership in the same genus)):

congenator, congener, congeneric

WordNet sense 3 (properly related in size or degree or other measurable characteristics; usually followed by `to'):

proportional

WordNet sense 4 (having significance only in relation to something else):

comparative