Emily Dickinson Lexicon

LISP, v.i. [G. lispeln, D. lispen, to lisp; Sax. vlisp or vlips, a lisping; Sw. läspa, Russ. lepetzu, to lisp.]

To speak with a particular articulation of the tongue and teeth, nearly as in pronouncing th. Lisping is particularly noticed in uttering th for s, as, yeth for yes. It is most common in children. I lisped in numbers, for the numbers came. – Pope.