Definition of "agin"

agin

/ə.ˈɡɪn/

adverb
not comparable
1. (colloquial or now often humorous) Alternative form of again
  Quotations
  At which juncture, he exclaimed, in a voice of dire exasperation : “Bust me, if she ain't at it agin !”
  1859, Charles Dickens, “A Tale of Two Cities”, in All the Year Round, volume 1, page 98
preposition
1. (dialectal, colloquial, or now often humorous) Alternative form of against
  Quotations
  [The Court] said: "Young man, this ere Court is satisfied that there ain't nothin' in the laws of Vermont agin tippin' over a churn full of sap. […] But I want ye should remember one thing—that this ere Court has made up his mind that it's a very naughty trick, and it's a shame that there's so many maple-trees in the State, and no law agin tippin' over sap."
  1859, Harper's New Monthly Magazine, volume 19, page 278
  when I got to that old shackly brick store by the Temperance Tavern, I backed up agin the wall to have another think.
  1876, Mark Twain, The Adventures of Tom Sawyer, page 228
  [Howland Owl:] Boy! There's prejudice for you... I got a pure, pristine boy here an' you're agin him. [Porky Pine:] I ain't AGIN him... I jus' ain't FOR him...
  1960 September 22, Walt Kelly, Pogo, comic strip, page 183