To smile, parting the lips so as to show the teeth.
Why do you grin? Did I say something funny?
To express by grinning.
She grinned pleasure at his embarrassment.
To show the teeth, like a snarling dog.
To grin as part of producing a particular facial expression, such as a smile or sneer.
He grinned a broad smile when I told him the result.
The act or expression of one who grins.