What does nec nōn mean in Latin?

nec nōn, a conjunction, means “and also, and indeed, and certainly, not to mention”.

How do you pronounce nec nōn?

In classical Latin, [ˈnɛk ˈnoːn]; in ecclesiastical (church) Latin, [ˈnɛk ˈnɔn].

conjunction · neuter

Classical[ˈnɛk ˈnoːn]Ecclesiastical[ˈnɛk ˈnɔn]

and also, and indeed, and certainly, not to mention
Certe, inquit Merula; nam ibi vidi greges magnos anserum, gallinarum, columbarum, gruum, pavonum, nec non glirium, piscium, aprorum, ceterae venationis.“Certainly,” said Merula, “for I saw there great flocks of geese, chickens, pigeons, cranes, peacocks, not to mention sparrows, fish, boar, and other game.”116 BCE – 27 BCE, Marcus Terentius Varro, Rerum rusticarum 3.14
sunt tibi regna patris Dauni, sunt oppida captaYou have the realms of your father Daunus, the many towns taken by your hand, and Latinus also has gold and spirit29 BCE – 19 BCE, Vergilius, Aeneis 12.22–23

From nec (“and not, nor”) + nōn (“not”).