noun

1. Philos.
   1. the denial of the existence of any basis for knowledge or truth
   2. the general rejection of customary beliefs in morality, religion, etc.
      also ethical nihilism
2. the belief that there is no meaning or purpose in existence
3. Politics
   1. the doctrine that existing social, political, and economic institutions must be completely destroyed in order to make way for new institutions
   2. a movement in Russia (c. 1860-1917) which advocated such revolutionary reform and attempted to carry it out through the use of terrorism and assassination
   3. loosely any violent revolutionary movement involving the use of terrorism

Etymology: < L nihil (see nihil) + -ism