Synonymous means having the same or nearly the same meaning as another word. “Happy” and “joyful” are synonymous because they express the same feeling. “Large” and “big” are synonymous words you might swap in a sentence without changing what you mean.

When you're writing and want to avoid repeating the same word too many times, you look for a synonym, which is a word that's synonymous with the one you've been using. If you've written “beautiful” three times in one paragraph, you might replace it with “lovely” or “gorgeous,” which are synonymous with it.

The word can also describe things that have become so closely connected that people think of them as the same. Someone might say that a particular athlete's name has become synonymous with excellence in their sport, meaning you can't think of one without thinking of the other. A company known for innovation might become synonymous with cutting-edge technology. When two things are synonymous, they're so closely linked in people's minds that mentioning one immediately brings the other to mind.