The term 'barrel stopper' refers to a device used to seal the opening of a barrel or other container. The two crossword solutions for this term are 'BUNG' and 'WHOA'. BUNG is a noun that refers to a stopper, usually made of wood or metal, that is used to close the opening of a barrel or cask. WHOA is an interjection that is used to express surprise or to stop someone or something from moving. Both words can be used to refer to the same device, which is used to seal the opening of a barrel or other container.