It largely has an alcoholic content (3)
I believe the answer is:
tun
'an alcoholic content' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'it largely' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'largely' becomes 'un' (I am not sure about this - if you are sure you should believe this answer much more).
't'+'un'='TUN'
'has' acts as a link.
Can you help me to learn more?
(Other definitions for tun that I've seen before include "'Large cask, for beer perhaps (3)'" , "Barrel holding many gallons" , "One can hold wine" , "Container of beer" , "butt" .)