a character in Alice's Adventures in Wonderland by Lewis Carroll, which disappears very slowly until only its big smile is left. People sometimes say someone is "grinning like a Cheshire cat" to mean that they have a big and rather silly smile on their face.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
Dictionary pictures of the day
Do you know what each of these is called?
Click on any of the pictures above to find out what it is called.