lackwit

A witless person; a fool.

Fear flashed through Tom's eyes as the lackwit looked to the housekeeper.

“Enunciation, Piper. Enunciation. Don't make people think you're a lackwit.”

Foolish; idiotic or simple-minded.

An evil, however, accompanied the benefit; shoals of worthless authors sprang up, and you may still perceive the garreteer drawing upon his lackwit brain for some production, the labour of which he expects will be paid by the declaration of his country, that a second Boileau, a Montesquieu, or a Racine has at length appeared.

One wall was painted with the story of St Robert the hermit and his persecution by Sir William de Stuteville, while the other depicted the cowherd Caedmon, albeit looking too lackwit to herd a hen let alone wax lyrical.