Merriam-Webster Collegiate Dictionary - relative

 I. noun  Date: 14th century  1. a word referring grammatically to an antecedent  2. a thing having a relation to or connection with or necessary dependence on another thing  3.  a. a person connected with another by blood or affinity  b. an animal or plant related to another by common descent  4. a ~ term  II. adjective  Date: 15th century  1. introducing a subordinate clause qualifying an expressed or implied antecedent a ~ pronoun; also introduced by such a connective a ~ clause  2. relevant, pertinent matters ~ to world peace  3. not absolute or independent ; comparative the ~ isolation of life in the country  4. having the same key signature — used of major and minor keys and scales  5. expressed as the ratio of the specified quantity (as an error in measuring) to the total magnitude (as the value of a measured quantity) or to the mean of all the quantities involved