synonymicon
http://www.wordnik.com/words/synonymicon

(noun) A dictionary of synonymous words.

(noun) A thesaurus.

'Synonymicon' is made up of 'synonym,' which comes from the Greek word meaning 'word having the same sense as another,' and the Greek 'eikon,' likeness, image, portrait.

 

Example:
"Some of those early dictionaries, or lexicons, were arranged not alphabetically by word but by subject; some were simply dictionaries of difficult words; some merely sRead More...