You thought you knew everything?! (8)

There are only four words in the English language which end in 'dous': tremendous, horrendous, stupendous, and hazardous.

(You're not possibly doubting this, are you?)

There are two words in the English language that have all five vowels in order: 'abstemious' and 'facetious.'

(Check them out: a e i o u)