Litotes is the use of a negated antonym to make an understatement or to emphatically affirm the positive.
In John 6:37 in the Bible, the clause I will in no wise cast out means "I will certainly receive."
An expression of the form not unX, as in the following:
Moreover, the attempt is not unsuccessful. (Eduard Schevardnadze)
This page is an extract from the LinguaLinks Library. Version 5.0 published on CD-ROM by SIL International, 2003.