Rainstorm country! (4)

I believe the answer is:

iran

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This might be a double definition.

'rainstorm' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'country' is the second definition.
(Iran is a country)

Can you help me to learn more?

(Other definitions for iran that I've seen before include "Middle Eastern country" , "It was known as Persia until 1935" , "Modern-day Persia" , "oil supplier" , "Country that was Persia" .)

I've seen this clue in the Evening Standard.

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