A good sport is someone who accepts in good spirit or good humour, being beaten at something: someone who loses gracefully.
A good sport can also be someone who does not mind being laughed at when a joke or trick is played on them: someone who has a good sense of humour.
Examples of use:
a) She was very disappointed she didn't win the race, but she was a good sport about it.
b) He never complains when he loses a tennis match – he's such a good sport.
c) We are always playing tricks on our dad. We're lucky he's a good sport!
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