synonymist

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who studies or discriminates synonyms.

from The Century Dictionary.

• noun One who collects and explains synonyms; specifically, in natural history, one who collects the different names or synonyms of animals or plants.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who collects or explains synonyms.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person who studies synonyms.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a student of synonyms