Crossword Genius

Shortage of wind -- oxygen needed for asthmatic initially (7)

Ross

I believe the answer is:

drought

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'shortage' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

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(Other definitions for drought that I've seen before include "Period with little rain" , "Aridity" , "Lack of rain" , "Period of low rainfall" , "Lack of rainfall" .)

I've seen this clue in The Telegraph.
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