Source : Webster's Revised Unabridged Dictionary (1913)

Lexicology \Lex`i*col"o*gy\ (-j[y^]), n. [Gr. lexiko`n lexicon +
   -logy: cf. F. lexicologie.]
   The science of the derivation and signification of words;
   that branch of learning which treats of the signification and
   application of words.

Source : WordNet®

lexicology
     n : the branch of linguistics that studies the lexical component
         of language