Lewis & Short

rĕlātīvus, a, um, adj. [refero], having reference or relation, referring, relative (post-class.), Arn. 7, p. 221: qualitas, Mart. Cap. 5, § 451: appellatio, Aug. Trin. 5, 16.
In gram.: pronomen, Prisc. p. 1063 sq. P.
Adv.: rĕlātīvē, relatively: vicinus et amicus relative dicuntur, Aug. Trin. 5, 71.