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nemesis - noun (Greek mythology) the goddess of divine retribution and vengeance; something causes misery or death
nepotism - (noun) favoritism shown to relatives or close friends by those in power (as by giving them jobs)
nihilism - noun a revolutionary doctrine that advocates destruction of the social system for its own sake; complete denial of all established authority and institutions; the delusion that things (or everything, including the self) do not exist; a sense that everything is unreal
non sequitur - a conclusion not based logically on evidence, not based on premise
noxious - adj. injurious to physical or mental health