noun

• A device for projecting a hard object very forcefully; a firearm or cannon.
• A device for projecting a hard object very forcefully; a firearm or cannon.
• A device for projecting a hard object very forcefully; a firearm or cannon.
  "It was April 22, 1831, and a young man was walking down Whitehall in the direction of Parliament Street.[…]. He halted opposite the Privy Gardens, and, with his face turned skywards, listened until the sound of the Tower guns smote again on the ear and dispelled his doubts."
• (surfing) A long surfboard designed for surfing big waves (not the same as a longboard, a gun has a pointed nose and is generally a little narrower).
  "2000, Drew Kampion, surfline.com by the winter of 1962, the Brewer Surfboards Hawaii gun was the most in-demand big-wave equipment on the North Shore."

verb

• (transitive) To cause to speed up.
  "He gunned the engine."
• (informal) To offer vigorous support to (a person or cause).
  "We're all gunning for you."
• (informal) (gunning for something or gunning to do something) make a great effort.
  "Australian John Landy, one of Bannister’s rivals also gunning to break the four-minute barrier, took more than a second off the Briton’s time in Turku, Finland, a few weeks later."
• (ambitransitive, US, prison slang, of a male prisoner) Synonym of gun down (“to masturbate while making sustained eye contact with someone — typically a female prison officer — as a form of intimidation”).
  "[…] all inmates participated in such conduct, and […] "the inmates gunned only female staff, not the all-male security staff," he said."

noun

• (obsolete, slang) A magsman or street thief.
  "To discover […] how the honest poor are compelled to hob-and-nob with the “shoful pitcher” and the “gun,” it is necessary to visit the vast nursery-grounds of crime."