What is a word or phrase that means nearly the same as another word called?

A word or phrase that means nearly the same as another word is called a synonym. This term is essential in understanding language, as synonyms allow for a richer expression and variation in writing and speech. They can help avoid repetition and can provide nuanced meanings depending on the context in which they are used. For instance, the words "happy" and "joyful" are synonyms; they convey similar feelings but might evoke slightly different responses depending on the situation. Recognizing synonyms is a key part of vocabulary development and enhances communication skills.