I once knew a word that meant to mention something by announcing that you would not mention it. The word may be Greek; I encountered it in the study of poetry.
An example, then, from poetry, Edmund Spenser's Aegloga Quartet:
I will not match her with Latonaes seede.
Such follic great sorrow to Niobe did breede.
Now she is a stone,
And makes daily mone,
Warning all others to take heede.
Here the poet is publicly refusing to compare his subject, Elysa, with the goddess Latona, but in doing so (quite intentionally) makes the comparison.
This device is common in poetry, and I believe the term is most used in this regard, but is common in politics as well.