'Relative clause' definitions:

Definition of 'relative clause'

noun

A clause introduced by a relative pronoun; "`who visits frequently' is a relative clause in the sentence `John, who visits frequently, is ill'"

From: GCIDE

Relative \Rel"a*tive\ (r?l"?-t?v), a. [F. relatif, L. relativus. See Relate.]
1. Having relation or reference; referring; respecting; standing in connection; pertaining; as, arguments not relative to the subject. [1913 Webster]
I'll have grounds More relative than this. --Shak. [1913 Webster]
2. Arising from relation; resulting from connection with, or reference to, something else; not absolute. [1913 Webster]
Every thing sustains both an absolute and a relative capacity: an absolute, as it is such a thing, endued with such a nature; and a relative, as it is a part of the universe, and so stands in such a relations to the whole. --South. [1913 Webster]
3. (Gram.) Indicating or expressing relation; refering to an antecedent; as, a relative pronoun. [1913 Webster]
4. (Mus.) Characterizing or pertaining to chords and keys, which, by reason of the identify of some of their tones, admit of a natural transition from one to the other. --Moore (Encyc. of Music). [1913 Webster]
Relative clause (Gram.), a clause introduced by a relative pronoun.
Relative term, a term which implies relation to, as guardian to ward, matter to servant, husband to wife. Cf. Correlative. [1913 Webster]