Smiling
Part of speech: adjective
Definition: That which smiles or has a smile.
Part of speech: noun
Definition: The action of the verb to smile.
Part of speech: verb
Definition: To have (a smile) on one's face.
Example sentence: I never get tired of smiling. I'm just the kind of guy who likes to smile.
Grin
Part of speech: noun
Definition: A smile in which the lips are parted to reveal the teeth.
Part of speech: verb
Definition: To smile parting the lips so as to show the teeth.
Example sentence: When you know the truth is on your side, when you have dutifully paid all your taxes, but you are still targeted for non-payment of dues, then what do you do? You grin and bear the harassment because you have nothing to hide.