Daze caused by Stacy's first big barrel (4)

I believe the answer is:

stun

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'daze' is the definition.
(I know that daze can be written as stun)

'stacy's first big barrel' is the wordplay.
'stacy's first' becomes 's' (tst letter of 'stacy').
'big barrel' becomes 'tun' (tun is a kind of barrel. I am not sure about the 'big' bit.).
's'+'tun'='STUN'

'caused by' acts as a link.

Can you help me to learn more?

(Other definitions for stun that I've seen before include "Confound" , "Numb with nuts" , "Knock out temporarily" , "Make dazed or numb" , "Nuts (anag)" .)

I've seen this clue in The Independent.

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