Conclusive evidence of strength of liquor (5)
I believe the answer is:
proof
This clue could be a double definition.
'conclusive evidence' is the first definition.
(I've seen this in another clue)
'strength of liquor' is the second definition.
'proof' can be an answer for 'strength' (I've seen this before). I'm not sure about the 'of liquor' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for proof that I've seen before include "Specimen" , "Incontrovertible evidence" , "whisky's strength?" , "Strength of spirit" , "Evidence that establishes the truth" .)