the expression that you have on your face when you are happy, amused, etc. in which the corners of your mouth turn upward “Oh, hello,” he said, with a smile. She gave a wry smile. He had a big smile on his face. I'm going to wipe that smile off your face (= make you stop thinking this is funny).
Idioms looking very happy, especially soon after you have been looking worried or sad Twelve hours later she was all smiles again. See smile in the Oxford Advanced Learner's DictionaryCheck pronunciation:
smile