Pulpgrinder Thesaurus Rex contains a database of over 150,000 words. It encodes many different word relationships, not just synonyms.

Any highlighted (blue) word can be clicked to use it as the starting point for a new search, allowing you to focus more closely on your intended meaning.

Thesaurus Rex also encodes some indirect relationships. Among other connections, this "See also" section shows many terms from heraldry (related to the rose's use in coats of arms and the like).