Unambiguous measure of volume curate's drunk (5-3)

I believe the answer is:

clear-cut

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'unambiguous' is the definition.
(I've seen this before)

'measure of volume curate's drunk' is the wordplay.
'measure of volume curate's' becomes 'clear' (I am not sure about this - if you are sure you should believe this answer much more).
'drunk' becomes 'cut' (I've seen this before).
'clear'+'cut'='CLEAR-CUT'

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(Other definitions for clear-cut that I've seen before include "Syrian city" , "Well defined" , "Distinct and sharply-defined" , "Sharp" , "Definite - 2 down" .)

I've seen this clue in The Guardian.

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