PIE base ‘not’, root of prefix un- in Old English and German, in- in Latin, and a-, an- in Greek and Sanskrit. See also *ant-, root of un-, as in ‘undo’, indicating reversal or removal.
Other derivatives include negate, neglect, nothing, neuter, never, null, annul, deny, annihilate, renegade, negligee, naughty, nice, originally ‘ignorant, foolish, silly, senseless’, cognate with science.
[Pokorny *nĕ-1, nē, nei, pp. 756–758.]