Trepidatious is apparently not a word*

I love language. Learned this the other day. Follow the steps... (* in the prescriptivist sense. It is obviously a word by usage.)
  1. There's an old word "Trepid". OED calls it "rare" meaning nobody really uses it anymore. It is an adjective.
    Fun fact: from Latin, related to "trep-" "to tremble".
  2. Aside: From trepid we get the much more common word "Intrepid."
    Not "rare" at all.
  3. Trepid has a noun form "Trepidation" from the Latin Trepidare → Trepidationem.
  4. In English we often make an adjective out of a noun by add by -ious.
    Ambitious. Envious. Glorious. Studious. Vacatious. Just kidding about that last one but seriously it should be a word.
  5. So from the noun trepidation we convert to the adjective form "Trepidatious." But trepid was already an adjective.
    OED calls it "colloquial" which means "we here at oxford are judging you."
  7. Aside: spells it "Trepidacious" but Merriam-Webster, American Heritage and OED spell it with a T and the iPhone spell checker agrees. YMMV.