a priori

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

• adjective Proceeding from a known or assumed cause to a necessarily related effect; deductive.
• adjective Derived by or designating the process of reasoning without reference to particular facts or experience.
• adjective Knowable without appeal to particular experience.
• adjective Made before or without examination; not supported by factual study.

from The Century Dictionary.

• noun From the former; from that which precedes; hence, from antecedent to consequent, from condition to conditioned, or from cause to effect.

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

• (Logic) Characterizing that kind of reasoning which deduces consequences from definitions formed, or principles assumed, or which infers effects from causes previously known; deductive or deductively. The reverse of a posteriori.
• (Philos.) Applied to knowledge and conceptions assumed, or presupposed, as prior to experience, in order to make experience rational or possible.

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

• adjective law Known ahead of time.
• adjective logic Based on hypothesis rather than experiment.
• adjective Self-evident, intuitively obvious
• adjective Presumed without analysis
• adverb logic In a way based on theoretical deduction rather than empirical observation

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

• adjective based on hypothesis or theory rather than experiment
• adjective involving deductive reasoning from a general principle to a necessary effect; not supported by fact
• adverb derived by logic, without observed facts