Presumption

1. Behavior or attitude that is boldly arrogant or offensive; effrontery.
2. The act of presuming or accepting as true.
3. Acceptance or belief based on reasonable evidence; assumption or supposition.
4. A condition or basis for accepting or presuming.
5. Law. A conclusion derived from a particular set of facts based on law, rather than probable reasoning.

References:
"presumption." The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. Answers.com 07 Mar. 2007. http://www.answers.com/topic/presumption