A hold that makes you gasp outright! (5)

I believe the answer is:

grasp

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'a hold' is the definition.
('grasp' can be a synonym of 'hold')

I cannot understand how the rest of the clue works.

(Other definitions for grasp that I've seen before include "Understand; take in hand" , "Take firm hold" , "Hold - understanding" , "Catch on" , "Comprehension" .)

I've seen this clue in the Evening Standard.

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