A powerful grip, useful in defence (10)

I believe the answer is:

stronghold

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'useful in defence' is the definition.
'stronghold' can be an answer for 'defence' (stronghold is a kind of defence). I am not sure about the 'useful in' bit.

'a powerful grip' is the wordplay.
'a powerful' becomes 'strong' (I've seen this before).
'grip' becomes 'hold' (synonyms).
'strong'+'hold'='STRONGHOLD'

Can you help me to learn more?

(Other definitions for stronghold that I've seen before include "Defence" , "castle" , "Fortress" , "Keep" .)

I've seen this clue in The Irish News.

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