Lot of warning about barrel (7)
I believe the answer is:
fortune
'lot' is the definition.
('fortune' can be a synonym of 'lot')
'warning about barrel' is the wordplay.
'warning' becomes 'fore' (I've seen this in other clues).
'about' is an insertion indicator.
'barrel' becomes 'tun' (tun is a kind of barrel).
'fore' placed around 'tun' is 'FORTUNE'.
'of' is the link.
(Other definitions for fortune that I've seen before include "Great accumulation of wealth" , "Big bucks - fate" , "large sum of money" , "'. . . . . . . favours the brave'" , "Fate, destiny" .)