From WordNet (r) 3.0 (2006):
reason
n 1: a rational motive for a belief or action; "the reason that
war was declared"; "the grounds for their declaration"
[syn: reason, ground]
2: an explanation of the cause of some phenomenon; "the reason a
steady state was never reached was that the back pressure
built up too slowly"
3: the capacity for rational thought or inference or
discrimination; "we are told that man is endowed with reason
and capable of distinguishing good from evil" [syn: reason,
understanding, intellect]
4: the state of having good sense and sound judgment; "his
rationality may have been impaired"; "he had to rely less on
reason than on rousing their emotions" [syn: rationality,
reason, reasonableness]
5: a justification for something existing or happening; "he had
no cause to complain"; "they had good reason to rejoice"
[syn: cause, reason, grounds]
6: a fact that logically justifies some premise or conclusion;
"there is reason to believe he is lying"
v 1: decide by reasoning; draw or come to a conclusion; "We
reasoned that it was cheaper to rent than to buy a house"
[syn: reason, reason out, conclude]
2: present reasons and arguments [syn: argue, reason]
3: think logically; "The children must learn to reason"