Keep below decks (4)

I believe the answer is:

hold

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'keep' is the definition.
(both can mean to have or possess something)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for hold that I've seen before include "Keep; cargo space" , "Have or possess" , "Retain" , "Keep; part of ship" , "Keep in one's grasp" .)

I've seen this clue in the Evening Standard.

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