to pronounce the sibilant letter s imperfectly; to give s and z the sound of th; -- a defect common among children.-to speak with imperfect articulation; to mispronounce, as a child learning to talk.-to speak hesitatingly with a low voice, as if afraid.-to pronounce with a lisp.-to utter with imperfect articulation; to express with words pronounced imperfectly or indistinctly, as a child speaks; hence, to express by the use of simple, childlike language.-to speak with reserve or concealment; to utter timidly or confidentially; as, to lisp treason.-the habit or act of lisping. see lisp, v. i., 1.