Sea monster, not working for the Knight of the shears (8)

I believe the answer is:

seamster

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'the knight of the shears' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'sea monster not working' is the wordplay.
'not' suggests deleting specific letters.
'working' becomes 'on' (on can mean working or activated).
'monster' with 'on' removed is 'mster'.
'sea'+'mster'='SEAMSTER'

'for' is the link.

Can you help me to learn more?

(Another definition for seamster that I've seen is " One who sews".)

I've seen this clue in The Hindu.

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