kilderkin
From The Oxford Companion to Beer
is a cask or keg half the size of a UK barrel, holding 18 UK gal (81.83 l) or 22.5 US gallons. Manual handling weight legislation in the UK has made this cask the largest beer container in general commercial use for drayman (i.e., the person who delivers beer on behalf of a brewery) deliveries. Once a common sight in pub cellars, the kilderkin is now relatively rare.
This definition is from The Oxford Companion to Beer, edited by Garrett Oliver. © Oxford University Press 2012.