ain't

1706, originally a contraction of am not, and considered proper as such until in early 19c. it began to be also a generic contraction of are not, is not, has not, etc. This was popularized in representations of London cockney dialect in Dickens, etc., which led to the word being banished entirely from correct English. Bartlett ("Dictionary of Americanisms," 1848) reports that hain't for "have not" is "A contraction much used in common conversation in New England."