► reason the cause or fact that explains why something has happened or happens, or why someone has done something: “Why did you tell him?” “Oh, I had my reasons (=had a secret reason for doing it).” She sold the house for reasons best known to herself, (=for reasons other people do not understand).
► explanation a reason for why something happened or why you did something, especially one in which you give details: Is there any explanation for his behavior?
► excuse a reason that you give for why you did something bad: I hope she has a good excuse for being late again.
► motive a reason that makes someone do something, especially something bad: The police have found no motive for the attack.
► grounds a good reason, based on laws or rules, for doing, believing, or saying something. Used in legal or official language: Abusive behavior is grounds for divorce.
► justification a good reason that explains why someone has done something bad: The justification for the war was the fear that the enemy had nuclear weapons.
► rationale formal the reasons and ideas on which a decision, plan, etc. is based: What is the rationale for restricting the role of women in the military?
► pretext a false reason that you give for doing something, because you want to hide the real reason: He said he was sick, but it was just a pretext to get her to come visit him.