Source : Webster's Revised Unabridged Dictionary (1913)

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.