Only a real asshole whould expect a highschool kid to know this word which I never
saw before, and do not expect to see again.
restiform
adj.
ModL restiformis < L restis, rope (for IE base see RUSH2) + 3formis, 3FORM6 ropelike or cordlike; specif., designating either of two cordlike bundles of nerve fibers (restiform bodies) connecting the medulla oblongata with each hemisphere of the cerebellum

But, Dr. Bill, don't you think that if you heard the word pronounced you'd be able to guess the spelling, even if you hadn't heard it before? I admit some of the spelling-bee ones are really weird but this one is pretty phonetic.

Dear Bean: That is such a recondite neurology word that I never heard it before.
The kids in spelling bees ought not be expected to know words used only by a
few medical specialists. Christ, there tens of thousands of them.
And I cannot imagine kids being able to master words without learning their roots
as mnemonic guides to spelling. "Rh-" sounds like "r". Though no "rhest-" words.

this one is pretty phonetic.

Therein lies its trickiness. Who'd think it was so easy?
Restiform, Ar aitch ee ess tee eye pee aitch oh ar em, restiform.