They play a game happily.
Meaning: This means they are having fun and enjoying themselves while playing the game.
Choice of Words: Play is a verb that means to engage in an activity for enjoyment or recreation. Happily is an adverb that means in a happy or joyful way. When you put them together, "Play a game happily" means they are engaging in an activity for enjoyment or recreation in a happy and joyful way.
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Related Expressions