Acknowledge solver with expression of gratitude (8)

I believe the answer is:

thankyou

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'expression of gratitude' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'acknowledge solver' is the wordplay.
'acknowledge' becomes 'thank' (I've seen this in another clue).
'solver' becomes 'you' (the person solving the crossword).
'thank'+'you'='THANKYOU'

'with' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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