How to turn desperate (2,3)

I believe the answer is:

at bay

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'desperate' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?

I can't explain the remainder of the clue.

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(Other definitions for at bay that I've seen before include "Forced to turn and face the attackers" , "Cornered, trapped" .)

I've seen this clue in the Evening Standard.

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