1. The action of taking upon oneself of more than is warranted by one's position, right, or ability; forward or over-confident opinion or conduct; arrogance, pride, effrontery, assurance: Little Timmy had the presumption to answer the principal's question in quite a nasty and insolent way.
2. The assumption of taking something for granted, also that which is assumed to be, or to be true, on probable evidence; a belief deduced from facts or experience; assumed probability, supposition, expectation: Mr. Timmons made his presumptions of the issue at hand before he knew all the information concerning the circumstances of the problem.
3. In law, the inference of a fact not certainly known: The statement that James was guilty was just a presumption because not all the details concerning the case were known and proven.
4. In law, the assumption of the truth of anything until the contrary is proved or an inference established by the law as universally applicable to certain circumstances: The presumption that a defendant is innocent of committing murder is given until he or she is proven guilty.
5. A reason for believing; likely evidence: The presumption that Tom kicked his ball through the neighbor's window was probable because he was playing ball in his backyard at the time when the neighbor's window was broken!