means The complete absence of anything — no matter, no thought, no existence whatsoever — or the philosophical concept of that absolute void.

from A doubled-up English construction: 'nothing' (itself a fusion of Old English 'na thing,' literally 'not a thing') plus the suffix '-ness,' which turns adjectives and nouns into states or qualities. So the word literally builds 'the state of not-a-thing-ness' — layering negation upon negation until you arrive at the abstract noun for the void. Philosophers later borrowed it to translate weightier terms like the German 'das Nichts,' the kind of word Heidegger liked to brood over.