Wasn't Dumb and Dumberer the title of a movie?

Yes it was a prequel to dumb and dumber. Dumberer was a more apt title.

This from OED

O.E. dumb "silent, unable to speak," from PIE *dheubh- "confusion, stupefaction, dizziness." O.E., Goth. (thumb) and O.N. (dumbr) forms meant only "mute, speechless;" in O.H.G. (thumb) it meant both this and "stupid," and in Mod.Ger. this latter became the only sense. Meaning "foolish, ignorant" was occasionally in Eng. from c.1323, but modern use (1823) comes from infl. of Ger. dumm. Applied to silent contrivances, hence dumbwaiter (1749).