Fertile patch for a group (5)

I believe the answer is:

oasis

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'fertile patch' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

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(Other definitions for oasis that I've seen before include "source of water" , "Peaceful area away from trouble" , "Fertile place like waterhole in desert" , "Place of refreshment" , "water you'll want here" .)

I've seen this clue in The Mirror and The Daily Express.

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