Source : Webster's Revised Unabridged Dictionary (1913)

Lexicologist \Lex`i*col"o*gist\ (-k[o^]l"[-o]*j[i^]st), n.
   One versed in lexicology.

Source : WordNet®

lexicologist
     n : a compiler or writer of a dictionary; a student of the
         lexical component of language [syn: {lexicographer}]