1
general::
A statement that seems to contradict itself, with one part of it denying another. For example, I've always believed that "a poor millionaire" was a contradiction in terms. [Late 1700s]
American Heritage Idioms
2
general::
Phrase(s): a contradiction in terms
a statement containing a seeming contradiction. • A wealthy pauper is a contradiction in terms. • A straight-talking politician may seem to be a contradiction in terms.
McGrawhill's American Idioms And Phrasal Verbs