The Collaborative International Dictionary of English v.0.48:

Illapse \Il*lapse"\, n. [L. illapsus. See Illapse, v. i.]
   A gliding in; an immisson or entrance of one thing into
   another; also, a sudden descent or attack. --Akenside.
   [1913 Webster]

         They sit silent . . . waiting for an illapse of the
         spirit.                                  --Jeffrey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Illapse \Il*lapse"\, v. i. [imp. & p. p. Illapsed; p. pr. &
   vb. n. Illapsing.] [L. illapsus, p. p. of illabi; pref. il-
   in + labi to fall, slide.]
   To fall or glide; to pass; -- usually followed by into.
   --Cheyne.
   [1913 Webster]