Good reason is a commonly used term to describe a rationale or justification for something. There are many synonyms that can be used in place of this term to add variety to your writing or speech. Some alternatives to consider include logic, basis, motive, explanation, pretext, and cause. These words can be used interchangeably with "good reason" to convey a specific meaning or context. For example, instead of saying "I had a good reason to leave early", you could say "I had a logical explanation for leaving early". By using synonyms for "good reason", you can enhance your language skills and better express yourself in any situation.