Negation is a morphosyntactic operation in which a lexical item denies or inverts the meaning of another lexical item or construction.
A negator is a lexical item that expresses negation.
(Lexical Items [English])
Pei, Mario A., and Frank Gaynor. 1954.A dictionary of linguistics. New York: Philosophical Library.
Crystal, David. 1991.A dictionary of linguistics and phonetics. 3rd edition. Cambridge, MA: Basil Blackwell.