Quantity of booze: about one small cocktail? (4)
I believe the answer is:
cask
'quantity of booze' is the definition.
'cask' can be an answer for 'quantity' (cask is a kind of quantity). I am not sure about the 'of booze' bit.
'about one small cocktail?' is the wordplay.
'about' becomes 'ca' (short for circa).
'one small' becomes 's' (abbreviation - e.g. clothes size).
'cocktail?' becomes 'K' (the end letter or tail of the word 'cocktail').
'ca'+'s'+'k'='CASK'
Can you help me to learn more?
(Other definitions for cask that I've seen before include "Drink here" , "Wine vessel; sack (anag.)" , "Large barrel" , "Cylinder for liquid" , "Beer container" .)