The Collaborative International Dictionary of English v.0.48:

Lapse \Lapse\, v. i. [imp. & p. p. Lapsed; p. pr. & vb. n.
   Lapsing.]
   1. To pass slowly and smoothly downward, backward, or away;
      to slip downward, backward, or away; to glide; -- mostly
      restricted to figurative uses.
      [1913 Webster]

            A tendency to lapse into the barbarity of those
            northern nations from whom we are descended.
                                                  --Swift.
      [1913 Webster]

            Homer, in his characters of Vulcan and Thersites,
            has lapsed into the burlesque character. --Addison.
      [1913 Webster]

   2. To slide or slip in moral conduct; to fail in duty; to
      fall from virtue; to deviate from rectitude; to commit a
      fault by inadvertence or mistake.
      [1913 Webster]

            To lapse in fullness
            Is sorer than to lie for need.        --Shak.
      [1913 Webster]

   3. (Law)
      (a) To fall or pass from one proprietor to another, or
          from the original destination, by the omission,
          negligence, or failure of some one, as a patron, a
          legatee, etc.
      (b) To become ineffectual or void; to fall.
          [1913 Webster]

                If the archbishop shall not fill it up within
                six months ensuing, it lapses to the king.
                                                  --Ayliffe.
          [1913 Webster]

WordNet (r) 3.0 (2006):

lapsing
    n 1: a failure to maintain a higher state [syn: backsliding,
         lapse, lapsing, relapse, relapsing, reversion,
         reverting]