Cut off what dog wags? (7)

I believe the answer is:

curtail

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'cut off' is the definition.
(thesaurus)

'dog wags?' is the wordplay.
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'wags?' becomes 'tail' (I can't justify this - if you can you should believe this answer much more).
'cur'+'tail'='CURTAIL'

'what' acts as a link.

Can you help me to learn more?

(Other definitions for curtail that I've seen before include "Shorten, abridge" , "Cut short (an activity)" , "Cut short like canine appendage" , "Reduce in extent" , "make shorter" .)

I've seen this clue in the Sydney Morning Herald.

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