A large container in which drink is served, typically with a handle and spout. The waiter brought a flagon of wine to the table for the guests to share.
A large bottle for wine, liquors, etc. He reached for the flagon on the shelf to pour himself a drink.
(New Zealand, informal) A two-litre bottle of beer, usually sold for off-licence consumption. He stopped at the bottle shop and bought a flagon to take to the barbecue.