Crossword Genius

If one is in it, one is poor (4)

Ross

I believe the answer is:

need

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But I can't explain it at all! Could you help me understand?

(Other definitions for need that I've seen before include "Want - poverty" , "destitute state" , "privation" , "What's lacking" , "Want - require(ment)" .)

I've seen this clue in The Hindu.
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