(logic) a proposition that is true if and only if another proposition is false WordNet 3.0 & Open English WordNet

In logic, negation, also called the logical not or logical complement, is an operation that takes a proposition P {\displaystyle P} to another proposition "not P {\displaystyle P} ", standing for " P {\displaystyle P} is not true", written ¬ P {\displaystyle \neg P}, ∼ P {\displaystyle {\mathord {\sim }}P} or P ¯ {\displaystyle {\overline {P}}}. Wikipedia

Connective in logic and an operation computing that maps true to false and false to true. Wikipedia Disambiguation

Operation that takes a proposition p to another proposition "not p", written ¬p, which is interpreted intuitively as being true when p is false, and false when p is true; unary logical connective Wikidata

A proposition which is the contradictory of another proposition and which can be obtained from that other proposition by the appropriately placed addition/insertion of the word "not". (Or, in symbolic logic, by prepending that proposition with the symbol for the logical operator "not".). Wiktionary