Apparently there are only four words in English that end in 'dous'. My family and I have sussed out three of them: tremendous, stupendous, horrendous - at least we imagine that these words are acceptable. BUT ... we can't work out the fourth. Can any one help us?

I will (reluctantly) help you work it out -- this is one of those stupid conundrums that has gotten spread all over the 'net, but at least it's not as bad as the three words that end in -gry. In this case there are *many* words that end in -dous, but most aren't so common. if you do a OneLook search on *dous you will spot the 4th common one right away.

http://onelook.com