ni·hil·ism (n-lzm, n-) n.
a. An extreme form of skepticism that denies all existence.
b. A doctrine holding that all values are baseless and that nothing can be known or communicated.
2. Rejection of all distinctions in moral or religious value and a willingness to repudiate all previous theories of morality or religious belief.
3. The belief that destruction of existing political or social institutions is necessary for future improvement.
4. also Nihilism A diffuse, revolutionary movement of mid 19th-century Russia that scorned authority and tradition and believed in reason, materialism, and radical change in society and government through terrorism and assassination.
5. Psychiatry. A delusion, experienced in some mental disorders, that the world or one's mind, body, or self does not exist.
[Latin nihil, nothing; see ne in Indo-European Roots + -ism.]
source: The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004.