Which term refers to two or more words that have almost the same meaning?

The term that refers to two or more words that have almost the same meaning is "synonym." Synonyms are words that can be used interchangeably in many contexts because they convey similar meanings. For example, the words "happy," "joyful," and "elated" can often be used in place of one another without changing the overall meaning of a sentence.

In contrast, antonyms are words that have opposite meanings, which is not what the question is asking for. Homonyms are words that sound the same or are spelled the same but have different meanings, such as "bat" (the flying mammal) and "bat" (the sports equipment). Idioms are phrases that have a figurative meaning that is different from their literal meaning, like "kick the bucket," which means to die, rather than referring to the actual action of kicking a bucket. They do not fit the definition provided in the question.