Slang phrase nigger during the woodpile "a hid motive or not known factor affecting a scenario in an adverse way" [OED 1989] is attested by 1800; Thornton's "American Glossary" (1912) defines it as "A manner of accounting for the disappearance of gasoline," therefore "an unsolved mystery.In summary, the use of the word "Niga" isn't suitable, regard