chuckle
A quiet, gentle laugh when something is a little funny.
A chuckle is a quiet, gentle laugh that you make when something strikes you as funny or amusing, but not hilariously so. When you chuckle, you're not laughing out loud or slapping your knee: you're expressing amusement in a softer, more restrained way. You might chuckle at a clever joke in a book, at something silly your little brother does, or when you remember something funny that happened earlier in the day.
Chuckle can be a noun or a verb. Your grandfather might chuckle at an old story, or you might hear a chuckle coming from your teacher when a student makes a witty comment during class.
The word suggests warmth and good humor. A chuckle often means you find something pleasant or gently amusing rather than shocking or laugh-out-loud funny. Scientists might chuckle over a surprising result in their research. Friends might chuckle together over an inside joke. Unlike a full belly laugh that might make you double over, a chuckle is quiet enough that you could do it in a library without disturbing anyone.