"deny, make negative or null," 1795 (with an isolated use from 1620s), a back-formation from negation, or else from Latin negatus, past participle of negare, from PIE root *ne- "not." Related: Negated; negates; negating.
early 15c., negacioun, "an act of denial," from Old French negacion (12c.) and directly from Latin negationem (nominative negatio) "denial," noun of action from past-participle stem of negare "deny, say no," from PIE root *ne- "not." As "a negative assertion," mid-15c.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit a-, an- "not;" Avestan na "not;" Greek a-, an-, ne- "not;" Latin in- "not," ne "that not;" Old Church Slavonic and Lithuanian ne "not;" Old Irish an-, ni, Cornish ny "not;" Gothic and Old English un- "not."
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Harper, D. (n.d.). Etymology of negate. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/negate