What is Fun ?
Fun is (noun) enjoyable or amusing activity Having to stay in bed on my birthday is not much fun. Synonym amusement. Antonym boredom to have fun to enjoy yourself We had a lot of fun on the river. to make fun of someone or to poke fun at someone to laugh at someone Don’t make fun of her she’s trying her best. He poked fun at the Prime Minister. for fun as a joke She poured water down his neck for fun. Just for fun, he drove the car through town dressed as a gorilla. Why did you do that? Just for the fun of it! (adj) enjoyable, and probably involving games and laughter (informal.) Sitting on the grass in St James’s Park is a fun way of passing a Sunday afternoon. Synonym amusing. Antonym boring
source: Easier English, Student Dictionary Upper Intermediate Level