from The Century Dictionary and Cyclopedia
- n. (noun) A dictionary of synonymous words.
- n. (noun) A thesaurus.
from Wiktionary, Creative Commons Attribution/Share-Alike License
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 synonymicons, or synonym dictionaries.
Let's just take a look at a couple of non-new (at least 10 years old) synonymicons (yes, it's a rare but cultivated word for dictionary) for their descriptions.
'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.