nonnullus

Nonnullus, nonnulla, nonnullum is non plus nullus: a double negative that comes out positive, "not none", so "some, a fair few". It declines like nullus, which means the genitive singular is nonnullius and the dative nonnulli, the awkward unus nauta pattern shared by totus, solus and alius. In practice you meet it in the plural, where the endings are ordinary.

The tone is not neutral. Nonnulli implies a number worth mentioning, more than pauci and vaguer than aliquot, and it is the polite way of saying "quite a few people think" without naming them. Latin builds several such litotes: nonnumquam, "sometimes", and nonnihil, "somewhat". Say it as one word; the manuscripts often write non nulli split, which means the same thing.