fossa

Thanks, Doc! That's somethin' I never knew all these fossiliferous years of paleontologisizing!

from the AHD:

fossa

SYLLABICATION: fos·sa
PRONUNCIATION: fs
NOUN: Inflected forms: pl. fos·sae (fs)
Anatomy A small cavity or depression, as in a bone.
ETYMOLOGY: Latin, ditch, from feminine past participle of fodere, to dig.
OTHER FORMS: fossate (fst) —ADJECTIVE