mag ‧ num /ˈmæɡnəm/ BrE AmE noun [countable]
[ Sense 1: Date: 1700-1800 ; Language: Latin ; Origin: magnus 'great' ]
[ Sense 2: Date: 1900-2000 ; Origin: Magnum , a trademark ]
1 . a large bottle containing about 1.5 litres of wine, ↑ champagne etc
2 . a powerful type of gun that you can use with one hand:
a .44 magnum