nescio

Nescio, nescire, nescivi (or nescii), nescitum, fourth conjugation, and transparently ne plus scio, "I do not know". It takes a plain accusative for a thing, an accusative and infinitive for a reported fact, and an indirect question with the subjunctive when a question word follows.

That last point hides a trap. Nescio quis has frozen into a fixed phrase meaning "some one or other", and there the following verb stays indicative: nescio quid dixit is "he said something or other", while nescio quid dixerit is a real indirect question, "I do not know what he said". The mood is the only signal. Spanish necio, "foolish", descends from nescius, and so, by a long detour through French, does English nice.