Is it ensure, insure, or assure?
a cat with a broad grin, esp. fictitious
from Lewis Carroll's Alice's Adventures in Wonderland
A cat with an enormous grin encountered by Alice in Alice's Adventures in Wonderland, by Lewis Carroll. The cat tends to disappear, leaving only its smile hanging in the air.
Note: “Smiling like a Cheshire cat” refers to anyone with a conspicuous and long-lasting smile.