A lisp is a speech pattern where someone pronounces “s” and “z” sounds like “th” sounds instead. When someone with a lisp says “sun,” it might sound more like “thun.” When they say “zipper,” it comes out closer to “thipper.”

Many young children naturally have a lisp when they're first learning to talk, usually outgrowing it as their mouth muscles develop and they practice making different sounds. Some people keep a lisp into adulthood, though speech therapy can help if someone wants to change how they speak.

The word lisp itself demonstrates the sound pattern it describes: saying it with a lisp would make it sound like “lithp.” This makes the word a bit playful, though having a lisp is simply a variation in how someone speaks, not something wrong with them. Some famous actors, singers, and public speakers have had lisps without it affecting their success.

As a verb, to lisp means to speak with this pattern: “She lisped slightly when saying words with s sounds.” People sometimes use “lisp” more broadly to describe unclear or soft-sounding speech, but that's less precise.