Apophasis

n.

1.

(Rhet.) A figure by which a speaker formally declines to take notice of a favorable point, but in such a manner as to produce the effect desired. [For example, see Mark Antony's oration. Shak., Julius Cæsar, iii. 2.]

Noun

1.

apophasis - mentioning something by saying it will not be mentioned

rhetorical device