Oxymoron:
A figure of speech in which an author juxtaposes apparently contradictory terms. A rhetorical antithesis.


Example:
"Slave-holding Christians"
-Frederick Douglass in An American Slave


Explanation:
Douglass uses this oxymoron many times throughout his work. The purpose of this is to get his view that the people that were slave-holding Christians were hypocritical and immoral. The repetition of  this clues to the reader that Douglass is disgusted by the people that say this. The appendix of his autobiography has further information about this idea. All in all, this oxymoron shows how transparent the minds of the whites were during the time period, and didn't see that they were wrong.