Merriam-Webster Collegiate Dictionary - lisp

 I. verb  Etymology: Middle English, from Old English -wlyspian; akin to Old High German ~en to ~  Date: before 12th century  intransitive verb  1. to pronounce the sibilants s and z imperfectly especially by turning them into th and ??  2. to speak falteringly, childishly, or with a ~  transitive verb to utter falteringly or with a ~  • ~er noun  II. noun  Date: circa 1625  1. a speech defect or affectation characterized by ~ing  2. a sound resembling a ~ LISP  noun  Etymology: list processing  Date: 1959 a computer programming language that is designed for easy manipulation of data strings and is used extensively for work in artificial intelligence