Crossword Genius

Period, yet to finish, in aroused post-war amusement – dry it’s not! (5,5)

Ross

I believe the answer is:

water sport

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'period' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I cannot understand how the rest of the clue works.

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I've seen this clue in The Independent.
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