• gun [countable]

• 1 a metal weapon which shoots bullets or shells
• have/hold/carry a gun
• I could see he was carrying a gun.
• I've never fired a gun in my life.
• Jake was pointing a gun at the door.
• Two policemen were killed in a gun battle.
• 2

   put/hold a gun to somebody's head

• a) to put a gun very close to someone's head to shoot them or to force them to do something:
• He put a gun to her head and told the cashier to hand over the money.
• b) to force someone to do something they do not want to do:
• You chose to live here. Nobody put a gun to your head.
• 3 a tool that forces out small objects or a liquid by pressure:
• a paint gun
• a nail gun
• ➔ flashgun, spray gun
• 4 also starting pistol a gun which is fired into the air at the start of a race
• 5 American English informal

   big/top gun

  someone who is very important within an organization:
• Jed wanted to impress a Harvard professor and some other big guns.
• 6

   hired gun

  American English informal someone who is paid to shoot someone else
• 7

   with all guns blazing

  if you do something with all guns blazing, you do it with a lot of energy, determination, and noise
• ➔ son of a gun

   ; ➔ stick to your guns

   at stick1

   ; ➔ jump the gun

   at jump1 (11)

   ; ➔ be going great guns

   at great1 (11)

   ; ➔ spike somebody's guns

   at spike2 (6)

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.