Source : Webster's Revised Unabridged Dictionary (1913)

Euphemism \Eu"phe*mism\, n. [Gr. ? fr. ? to use word of a good
   omen; ? well + ? to speak: cf. F. euph['e]misme. See {Fame}.]
   (Rhet.)
   A figure in which a harts or indelicate word or expression is
   softened; a way of describing an offensive thing by an
   inoffensive expression; a mild name for something
   disagreeable.

Source : WordNet®

euphemism
     n : an inoffensive expression that is substituted for one that
         is considered offensive [ant: {dysphemism}]