nihilism

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Philosophy The doctrine that nothing actually exists or that existence or values are meaningless.
• noun Relentless negativity or cynicism suggesting an absence of values or beliefs.
• noun Political belief or action that advocates or commits violence or terrorism without discernible constructive goals.
• noun 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.
• noun Psychiatry A delusion, experienced in some mental disorders, that the world or one's mind, body, or self does not exist.

from The Century Dictionary.

• noun In metaphysics, the doctrine that nothing can really be known, because nothing exists; the denial of all real existence, and consequently of all knowledge of existences or real things.
• noun In theology, same as nihilianism.
• noun Total disbelief in religion, morality, law, and order.
• noun Originally, a social (not a political) movement in Russia, in opposition to the customary forms of matrimony, the parental authority, and the tyranny of custom. In this sense the word was introduced by Turgeneff in 1862. See nihilist, 3.
• noun Later, a more or less organized secret effort on the part of a large body of malcontents to overturn the established order of things, both social and political.

from the GNU version of the Collaborative International Dictionary of English.

• noun Nothingness; nihility.
• noun The doctrine that nothing can be known; scepticism as to all knowledge and all reality.
• noun (Politics) The theories and practices of the Nihilists.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun philosophy Extreme skepticism, maintaining that nothing has a real existence.
• noun ethics The rejection of all moral principles.
• noun politics (capitalized by protagonist Turgenev) A Russian anarchistic revolutionary doctrine (1860-1917) holding 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.
• noun The belief that all endeavors are ultimately futile and devoid of meaning.
• noun Contradiction (not always deliberate) between behavior and espoused principle, to such a degree that all possible espoused principle is voided.
• noun The deliberate refusal of belief, to the point that belief itself is rejected as untenable.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the delusion that things (or everything, including the self) do not exist; a sense that everything is unreal
• noun a revolutionary doctrine that advocates destruction of the social system for its own sake
• noun complete denial of all established authority and institutions