reason

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The basis or motive for an action, decision, or conviction. See Usage Notes at because, why.
2. n. A declaration made to explain or justify action, decision, or conviction: inquired about her reason for leaving.
3. n. An underlying fact or cause that provides logical sense for a premise or occurrence: There is reason to believe that the accused did not commit this crime.
4. n. The capacity for logical, rational, and analytic thought; intelligence.
5. n. Good judgment; sound sense.
6. n. A normal mental state; sanity: He has lost his reason.
7. n. Logic A premise, usually the minor premise, of an argument.
8. v. To use the faculty of reason; think logically.
9. v. To talk or argue logically and persuasively.
10. v. Obsolete To engage in conversation or discussion.
11. v. To determine or conclude by logical thinking: reasoned out a solution to the problem.
12. v. To persuade or dissuade (someone) with reasons.
13. idiom. by reason of Because of.
14. idiom. in reason With good sense or justification; reasonably.
15. idiom. within reason Within the bounds of good sense or practicality.
16. idiom. with reason With good cause; justifiably.

Century Dictionary and Cyclopedia

1. n. An idea acting as a cause to create or confirm a belief, or to induce a voluntary action; a judgment or belief going to determine a given belief or line of conduct. A premise producing a conclusion is said to be the reason of that conclusion; a perceived fact or reflection leading to a certain line of conduct is said to be a reason for that conduct; a cognition giving rise to an emotion or other state of mind is said to be a reason of or for that state of mind.
2. n. A fact, known or supposed, from which another fact follows logically, as in consequence of some known law of nature or the general course of things; an explanation.
3. n. An intellectual faculty, or such faculties collectively. The intellectual faculties collectively.
4. n. The logical faculties generally, including all that is subservient to distinguishing truth and falsehood, except sense, imagination, and memory on the one hand, and the faculty of intuitively perceiving first principles, and other lofty faculties, on the other.
5. n. The faculty of drawing conclusions or inferences, or of reasoning.
6. n. The faculty by which we attain the knowledge of first principles; a faculty for apprehending the unconditioned.
7. n. Intelligence considered as having universal validity or a catholic character, so that it is not something that belongs to any person, but is something partaken of, a sort of light in which every mind must perceive.
8. n. That which recommends itself to enlightened intelligence; some inward intimation for which great respect is felt and which is supposed to be common to the mass of mankind; reasonable measure; moderation; right; what mature and cool reflection, taking into account the highest considerations, pronounces for, as opposed to the prompting of passion.
9. n. A reasonable thing; a rational thing to do; an idea or a statement conformable to common sense.
10. n. The exercise of reason; reasoning; right reasoning; argumentation; discussion.
11. n. The intelligible essence of a thing or species; the quiddity.
12. n. In logic, the premise or premises of an argument, especially the minor premise.
13. n. By right or justice; properly; justly.
14. n. In French history, an act of worship of human reason, represented by a woman as the goddess of Reason, performed on November 10th, 1793, in the cathedral of Notre Dame, and also in other churches (renamed temples of Rea son) in France on that and succeeding days. The worship of Reason was designed to take the place of the suppressed Christian worship; recognition of the Supreme Being was restored through the influence of Robespierre.
15. n. Agreeable to reason; reasonable; just; proper; as, I will do anything in reason.
16. n. The human understanding; the discursive reason.
17. n. See do.
18. n. Synonyms Inducement, etc. (see motive), account, object, purpose, design.
19. To exereise the faculty of reason; make rational deductions; think or choose rationally; use intelligent discrimination.
20. To practise reasoning in regard to something; make deductions from premises; engage in discussion; argue, or hold arguments.
21. To hold account; make a reckoning; reckon.
22. To hold discourse; talk; parley.
23. To reason about; consider or discuss argumentatively; argue; debate.
24. To give reasons for; support by argument; make a plea for: often with out: as, to reason out a proposition or a claim.
25. To persuade by reasoning or argument.
26. To hold argument with; engage in speech or discussion; talk with; interrogate.
27. n. An obsolete spelling of raisin. In the following passage it is apparently applied to some other fruit than the grape.

Wiktionary

1. n. A cause:
2. n. uncountable Rational thinking (or the capacity for it; the cognitive faculties, collectively, of conception, judgment, deduction and intuition.
3. n. obsolete Something reasonable, in accordance with thought; justice.
4. n. mathematics, obsolete ratio; proportion.
5. v. intransitive To exercise the rational faculty; to deduce inferences from premises; to perform the process of deduction or of induction; to ratiocinate; to reach conclusions by a systematic comparison of facts.
6. v. intransitive Hence: To carry on a process of deduction or of induction, in order to convince or to confute; to formulate and set forth propositions and the inferences from them; to argue.
7. v. intransitive To converse; to compare opinions.
8. v. transitive To arrange and present the reasons for or against; to examine or discuss by arguments; to debate or discuss.
9. v. transitive, rare To support with reasons, as a request.
10. v. transitive To persuade by reasoning or argument.
11. v. transitive To overcome or conquer by adducing reasons.
12. v. transitive To find by logical process; to explain or justify by reason or argument.

GNU Webster's 1913

1. n. A thought or a consideration offered in support of a determination or an opinion; a just ground for a conclusion or an action; that which is offered or accepted as an explanation; the efficient cause of an occurrence or a phenomenon; a motive for an action or a determination; proof, more or less decisive, for an opinion or a conclusion; principle; efficient cause; final cause; ground of argument.
2. n. The faculty or capacity of the human mind by which it is distinguished from the intelligence of the inferior animals; the higher as distinguished from the lower cognitive faculties, sense, imagination, and memory, and in contrast to the feelings and desires. Reason comprises conception, judgment, reasoning, and the intuitional faculty. Specifically, it is the intuitional faculty, or the faculty of first truths, as distinguished from the understanding, which is called the discursive or ratiocinative faculty.
3. n. Due exercise of the reasoning faculty; accordance with, or that which is accordant with and ratified by, the mind rightly exercised; right intellectual judgment; clear and fair deductions from true principles; that which is dictated or supported by the common sense of mankind; right conduct; right; propriety; justice.
4. n. (Math.), obsolete Ratio; proportion.
5. v. To exercise the rational faculty; to deduce inferences from premises; to perform the process of deduction or of induction; to ratiocinate; to reach conclusions by a systematic comparison of facts.
6. v. Hence: To carry on a process of deduction or of induction, in order to convince or to confute; to formulate and set forth propositions and the inferences from them; to argue.
7. v. To converse; to compare opinions.
8. v. To arrange and present the reasons for or against; to examine or discuss by arguments; to debate or discuss.
9. v. rare To support with reasons, as a request.
10. v. To persuade by reasoning or argument
11. v. To overcome or conquer by adducing reasons; -- with down.
12. v. To find by logical processes; to explain or justify by reason or argument; -- usually with out.

WordNet 3.0

1. n. an explanation of the cause of some phenomenon
2. n. a justification for something existing or happening
3. v. think logically
4. n. the state of having good sense and sound judgment
5. v. decide by reasoning; draw or come to a conclusion
6. n. a rational motive for a belief or action
7. n. the capacity for rational thought or inference or discrimination
8. v. present reasons and arguments
9. n. a fact that logically justifies some premise or conclusion