Source : Webster's Revised Unabridged Dictionary (1913)

Backslide \Back`slide"\, v. i. [imp. {Backslid}; p. p.
   {Backslidden}, {Backslid}; p. pr. & vb. n. {Backsliding}.]
   [Back, adv. + slide.]
   To slide back; to fall away; esp. to abandon gradually the
   faith and practice of a religion that has been professed.

Source : WordNet®

backslide
     v : drop to a lower level, as in one's morals or standards [syn:
          {lapse}]
     [also: {backslidden}, {backslid}]

backslidden
     See {backslide}