The definite article is not wrong, but it is definitely odd there. Turn it around: Words that have the same meaning are synonyms.
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AnonymousI feel we could put the definite article "the" in front of the word "words"No. It's not normal to define an indefinite expression with a definite expression.
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Synonyms are the words that have the same __.
Anonymouswhat might be called an indefinte expression?No. By indefinite expression I meant, in essence, an indefinite noun phrase. Thus, the following are indefinite expressions. They typically do not refer to any specific instance of anything: