From The Collaborative International Dictionary of English v.0.48 :
barrelful \barrelful\ n.
The quantity that a barrel (of any size) will hold.
Syn: barrel.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
barrelful
n 1: the quantity that a barrel (of any size) will hold [syn:
barrel, barrelful]