to nullify (something) or make it ineffective or invalid
A slip at this stage could negate the whole experiment
to deny the existence or truth of (something)
Marx negated the … claim of capitalism to be the only possible natural system — Maurice Bloch
in grammar or logic, to make (a statement, clause, etc) negative
negater noun
negator noun
negatory /ʹneg-, niʹgaytəri/ adj
[Latin negatus, past part. of negare to say no, deny]