Varying measure of old Canary wine (4)
I believe the answer is:
sack
'old canary wine' is the definition.
'sack' can be an answer for 'wine' (sack is a kind of wine). I'm not certain of the 'old canary' bit.
'varying measure' is the wordplay.
'varying' becomes 'sac' (I can't explain this - if you can you should give a lot more credence to this answer).
'measure' becomes 'k' (k is a kind of measure).
'sac'+'k'='SACK'
'of' is the link.
Can you help me to learn more?
(Other definitions for sack that I've seen before include "Dismiss; plunder; wine" , "Elbow" , "It carries coal" , "boot" , "Fire the large bag?" .)