The Collaborative International Dictionary of English v.0.48:

Lexicologist \Lex`i*col"o*gist\
   (l[e^]ks`[i^]*k[o^]l"[-o]*j[i^]st), n.
   One versed in lexicology.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lexicologist
    n 1: a compiler or writer of a dictionary; a student of the
         lexical component of language [syn: lexicographer,
         lexicologist]