Definition of nihilism
1a : a viewpoint that traditional values and beliefs are unfounded and that existence is senseless and useless Nihilism is a condition in which all ultimate values lose their value.— Ronald H. Nash
b : a doctrine that denies any objective ground of truth and especially of moral truths
2a : a doctrine or belief that conditions in the social organization are so bad as to make destruction desirable for its own sake independent of any constructive program or possibility
b capitalized : the program of a 19th century Russian party advocating revolutionary reform and using terrorism and assassination