late 14c., realtif, in grammar, "a relative pronoun," from Old French relatif (13c.), from Late Latin relativus "having reference or relation," from Latin relatus, used as past participle of referre "bring back, bear back" (see refer), from re- "back, again" + lātus "borne, carried" (see oblate (n.)). The meaning "kinsman, kinswoman, person in the same family or connected by blood" is attested from 1650s.
early 15c., relatif, "having reference (to something), relating, depending upon," from Old French relatif and directly from Late Latin relativus "having reference or relation," from Latin relatus, used as past participle of referre "bring back, bear back" (see refer), from re- "back, again" + lātus "borne, carried" (see oblate (n.)).
Meaning "having mutual relationship, connected with each other" is from 1590s; that of "arising from or determined by relationship to something else" is from 1610s; that of "having or standing in a relation to something else" is from 1650s; that of "not absolute or existing by itself" is by 1704. In grammar, "referring to an antecedent," from 1520s.
1834, "fact or condition of being relative, existence as an immediate object of the understanding or experience, existence only in relation to a thinking mind," (apparently coined by Coleridge, in "Notes on Waterland's Vindication of Christ's Divinity"), from relative (adj.) + -ity. In scientific use, connected to the theory of Albert Einstein (1879-1955) having to do with the dependence of observation on the relative motion of observer and object, published in 1905 (special theory of relativity) and 1915 (general theory of relativity), but the word was used in roughly this sense by J.C. Maxwell in 1876. An earlier noun in the sense of "state of being relative" was relativeness (1670s).
1. "person who kills a parent or near relative" (1550s), also 2. "act of killing a parent or near relative" (1560s), both from French parricide (13c. in sense 1, 16c. in sense 2), from 1. Latin parricida, 2. Latin parricidium, probably from parus "relative" (a word of uncertain origin, but compare Greek paos, peos "relation," Sanskrit purushah "man") + 1. cida "killer," 2. cidium "killing," both from caedere "to kill, to cut down" (from PIE root *kae-id- "to strike"). Old English had fæderslaga. Related: Parricidal.