Most remorseful for shaking (6)

I believe the answer is:

tremor

I'm a little stuck... Click here to teach me more about this clue!

'shaking' is the definition.
(synonyms)

'most remorseful' is the wordplay.
'TREMOR' is hidden in amongst the letters.
But, I'm uncertain how the hidden word is indicated.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for tremor that I've seen before include "Quavering" , "Strong shake" , "feeling of excitement" , "Shudder - quake" , "Small shock" .)

I've seen this clue in The Mirror.

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