Source : Webster's Revised Unabridged Dictionary (1913)

Lisp \Lisp\ (l[i^]sp), v. i. [imp. & p. p. {Lisped} (l[i^]spt);
   p. pr. & vb. n. {Lisping}.] [OE. lispen, lipsen, AS. wlisp
   stammering, lisping; akin to D. & OHG. lispen to lisp, G.
   lispeln, Sw. l["a]spa, Dan. lespe.]
   1. To pronounce the sibilant letter s imperfectly; to give s
      and z the sound of th; -- a defect common among children.

   2. To speak with imperfect articulation; to mispronounce, as
      a child learning to talk.

            As yet a child, nor yet a fool to fame, I lisped in
            numbers, for the numbers came.        --Pope.

   3. To speak hesitatingly with a low voice, as if afraid.

            Lest when my lisping, guilty tongue should halt.
                                                  --Drayton.