platitudinous

Mark McLane attempted to use the term hebetudinous, however, in an example of hebetude he did so with atrocious spelling and grammar.

Blockheaded or thickheaded

Dense

Dumb

Dim-witted

Hebetudinous

Idiotic

All work and no play makes John a dull boy.

A word you could use in place of stupid:

brainless, dazed, dense, dim, doltish, dopey, dull, dumb, dummy, foolish, futile,gullible, half-baked, half-witted, idiotic, ill-advised, imbecilic, inane, indiscreet, insensate,irrelevant, laughable, loser*, ludicrous,meaningless, mindless, moronic, naive,nonsensical, obtuse, out to lunch, pointless,puerile, rash, senseless, shortsighted, simple, simpleminded, slow, sluggish, stolid, stupefied,thick, thick-headed, trivial, unintelligent, unthinking, witless, hebetudinous.