Real Dictionary

smile
countable noun: A smile is the expression that you have on your face when you smile.
verb: If you say that something such as fortune smiles on someone, you mean that they are lucky or successful.
verb: If you smile something, you say it with a smile or express it by a smile.
verb: When you smile, the corners of your mouth curve up and you sometimes show your teeth. People smile when they are pleased or amused, or when they are being friendly.

smile in American English
the act of smiling
to express with a smile
to have or take on a facial expression showing usually pleasure, amusement, affection, friendliness, etc., or, sometimes, irony, derision, etc. and characterized by an upward curving of the corners of the mouth and a sparkling of the eyes
intransitive verb: to assume a facial expression indicating pleasure, favor, or amusement, but sometimes derision or scorn, characterized by an upturning of the corners of the mouth
transitive verb: to assume or give (a smile, esp. of a given kind)

smile in British English
noun: a facial expression characterized by an upturning of the corners of the mouth, usually showing amusement, friendliness, etc, but sometimes scorn, etc
verb: to wear or assume a smile