nothing, nothingness / (Buddhism) mu; the null set: neither yes nor no (in response to a koan or other question that mistakenly assumes an affirmative or negative answer).

nothing / nothingness / none / nil / not

non-, un- / non-, un-

unreasonably, absurdly, recklessly, at random

not contacting for a while, a long silence

(phonetics) voiceless sound

meaningless

nonsense / meaninglessness

(informal) no problem

defenseless