Source : Webster's Revised Unabridged Dictionary (1913)

Fatty \Fat"ty\, a.
   Containing fat, or having the qualities of fat; greasy;
   gross; as, a fatty substance.

   {Fatty acid} (Chem.), any one of the paraffin series of
      monocarbonic acids, as formic acid, acetic, etc.; -- so
      called because the higher members, as stearic and palmitic
      acids, occur in the natural fats, and are themselves
      fatlike substances.

   {Fatty clays}. See under {Clay}.

   {Fatty degeneration} (Med.), a diseased condition, in which
      the oil globules, naturally present in certain organs, are
      so multiplied as gradually to destroy and replace the
      efficient parts of these organs.

   {Fatty heart}, {Fatty liver}, etc. (Med.), a heart, liver,
      etc., which have been the subjects of fatty degeneration
      or infiltration.

   {Fatty infiltration} (Med.), a condition in which there is an
      excessive accumulation of fat in an organ, without
      destruction of any essential parts of the latter.

   {Fatty tumor} (Med.), a tumor consisting of fatty or adipose
      tissue; lipoma.

Source : WordNet®

fatty acid
     n : any of a class of aliphatic monocarboxylic acids that form
         part of a lipid molecule and can be derived from fat by
         hydrolysis; fatty acids are simple molecules built around
         a series of carbon atoms linked together in a chain of 12
         to 22 carbon atoms