great gun
/ˈɡreɪt ˌɡʌn/noun
1A firearm or gun of such size that it needs to be mounted for firing; a piece of heavy ordnance. Now historical.
2 Figurative and in figurative contexts. A powerful or impressive person; a distinguished or eminent person.
3 great guns!: used as an exclamation expressing surprise or disbelief.
Phrases
to go great guns
Origin
Late Middle English; earliest use found in Geoffrey Chaucer (c1340–1400), poet and administrator. From great + gun.