Won’t share: had to drink initially enormous amount of alcohol (8)
I believe the answer is:
hogshead
'amount of alcohol' is the definition.
(large cask of alcohol)
'won't share had to drink initially enormous' is the wordplay.
'won't share' becomes 'hogs' (to hog something is to refuse to share it).
'to drink' means one lot of letters goes inside another.
'initially' indicates taking the first letters.
The first letter of 'enormous' is 'e'.
'had' going around 'e' is 'head'.
'hogs'+'head'='HOGSHEAD'
(Other definitions for hogshead that I've seen before include "barrel" , "Provider of brawn" , "Large cask for alcohol" , "A lot of wine" , "Large cask holding 54 gallons of beer" .)