You wrote: There are only four words in the English language which end in "dous": tremendous, horrendous, stupendous, and hazardous

According to Verbivore:

At least 32 additional dous words repose in various dictionaries: apodous, antropodous, blizzardous, cogitabundous, decapodous, frondous, gastropodous, heteropodous, hybridous, iodous, isopodous, jeopardous, lagopodous, lignipodous, molybdous, mucidous, multifidous, nefandous, nodous, octapodous, palladous, paludous, pudendous, repandous, rhodous, sauropodous, staganopodous, tetrapodous, thamphipodous, tylopodous, vanadous and voudous.

Verbivore also has a contest regarding words at this website:
http://www.salon.com/weekly/verb960624.html