Which of the following describes what synonyms must have in common?

Synonyms must have the same meaning.

Synonyms are words that have similar meanings. In order to be considered synonyms, words must have the same or similar denotations, or literal meanings. This means that they should refer to the same or similar concepts or objects. However, it is important to note that synonyms can have different connotations or shades of meaning, even though their denotations may be the same or similar.