gun 
(gŭn)
(gŭn)n.
1. A weapon consisting of a metal tube from which a projectile is fired at high velocity into a relatively flat trajectory, especially:
a. A portable firearm, such as a rifle or revolver.
b. A cannon with a long barrel and a relatively low angle of fire.
2. A device resembling a firearm or cannon, as in its ability to project something, such as grease or paint, under pressure or at great speed.
3. A discharge of a firearm or cannon as a signal or salute: heard the guns honoring the leader.
4. One who is armed with or skilled in the use of a gun.
5. The throttle of an engine, as of an automobile.
6. guns Slang The biceps muscles of the arms.
v. gunned, gun·ning, guns
v.tr.
1. To shoot (a person): a bank robber who was gunned down by the police.
2. To open the throttle of (an engine) so as to accelerate: gunned the engine and sped off.
v.intr.
Phrasal Verb: To hunt with a gun.
gun for
Idioms: 1. To plan or take action to harm or destroy (someone).
2. To go after in earnest; set out to obtain: gunning for a promotion.
go great guns
To proceed or perform with great speed, skill, or success.
hold a gun to (someone's) head
To put pressure on someone.
under the gun
Under great pressure or under threat.
[Middle English gonne, cannon, short for Gunilda, woman's name applied to a siege engine, from Old Norse Gunnhildr, woman's name : gunnr, war; see gwhen- in the Appendix of Indo-European roots + hildr, war.]