dialectology

from WordNet (r) 3.0 (2006)

dialectology
    n 1: the branch of philology that is devoted to the study of
         dialects

from The Collaborative International Dictionary of English v.0.48

Dialectology \Di`a*lec*tol"o*gy\, n. [Dialect + -logy.]
   That branch of philology which is devoted to the
   consideration of dialects. --Beck.
   [1913 Webster]