The Collaborative International Dictionary of English v.0.48:

AEsthetics \[AE]s*thet"ics\, Esthetics \Es*thet"ics\ (?; 277),
   n. [Gr. ? perceptive, esp. by feeling, fr. ? to perceive,
   feel: cf. G. [aum]sthetik, F. esth['e]tique.]
   The theory or philosophy of taste; the science of the
   beautiful in nature and art; esp. that which treats of the
   expression and embodiment of beauty by art.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Esthete \Es"thete\, n.; Esthetic \Es*thet"ic\, a., Esthetical
\Es*thet"ic*al\, a., Esthetics \Es*thet"ics\, n. etc.
   Same as [ae]sthete, [ae]sthetic, [ae]sthetical,
   [ae]sthetics, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

esthetics
    n 1: (art) the branch of philosophy dealing with beauty and
         taste (emphasizing the evaluative criteria that are applied
         to art); "traditional aesthetics assumed the existence of
         universal and timeless criteria of artistic value" [syn:
         aesthetics, esthetics]