The Collaborative International Dictionary of English v.0.48:

Etymologist \Et`y*mol"o*gist\ ([e^]t`[i^]*m[o^]l"[-o]*j[i^]st),
   n. [Cf. F. ['e]tymologiste.]
   One who investigates the derivation of words.
   [1913 Webster]

WordNet (r) 3.0 (2006):

etymologist
    n 1: a lexicographer who specializes in etymology