"No reason" refers to a situation where there is no discernible explanation or cause for something. Some synonyms for this phrase could include "without cause," "unjustified," "unwarranted," "groundless," "baseless," "senseless," "purposeless," and "arbitrary." These words can be used to describe situations where there is no clear justification for an action or decision. For example, someone may decline an invitation to a party for no reason, or a business may reject a proposal without cause. Using synonyms for "no reason" can help to add variety and clarity to your language, and accurately convey the meaning of your message.