li·to·tes 
(lītə-tēz′, lĭtə-, lī-tōtēz)
(lītə-tēz′, lĭtə-, lī-tōtēz)n. pl. litotes
A figure of speech consisting of an understatement in which an affirmative is expressed by negating its opposite, as in This is no small problem.
[Greek lītotēs, from lītos, plain; see lei- in the Appendix of Indo-European roots.]