synonymical

/ˌsɪnəˈnɪmɪkəl/
adjective
  1. Relating to or having the nature of a synonym; having a similar meaning (less common variant of 'synonymic').
    • He looked up the synonymical entries in the thesaurus.
    • The two phrases are not exactly synonymical in every situation.
    • The synonymical relationship between 'happy' and 'glad' is clear.