Yes, I am a linguistics geek.
I was driving to pick up my daughter today and thinking about the old meaning of the word "stupid," which was "stunned by grief or other strong emotion." Then it struck me that this word was probably related to the word "stupor." So I tried to think of some other examples of words with this -id/-or pattern, and within a minute or so I'd come up with valid/valor - except I wasn't sure if my extrapolation was (pardon me for this one) valid.
So after dinner tonight I pulled out my etymological dictionary (everybody should have one! :-) ) and I checked it out.
This pattern is bigger than I suspected.
The -id suffix makes adjectives out of old Latin verbs, while the -or (-our, for Brits) suffix makes nouns. Not every -id word has a corresponding -or word, nor does every -or word have an -id word, but check this out:
stupid / stupor
vapid / vapor
valid / valor
candid / candor
fervid / fervor
rigid / rigor
splendid / splendor
rancid / rancor
torpid / torpor
Valid/valor, the one I'd been wondering about, comes from the Latin vale, "to be strong or well."
I thought of another one, too: languid / languor
For interest's sake, I'll give you the ones that don't have correspondents:
-id: torrid, acid, fluid, morbid, gravid
-or: ardor, clamor, color, dolor, favor, honor, labor, odor, savor