<grisom> I can't tell yous how disappointed I am that "gideous" is not a word.
<tezcatlipoca> Hey, umu, why can't we simply make gideous a word? What would such a word mean, in English?
* umunmutamku arrives in a puff of faggy smoke
<umunmutamku> Well! Let's start from our model-word.
<umunmutamku> It would appear that 'hideous' started out as ME hidous < Old French hidos < hisdos (the further Latin affinities are very unlikely-sounding); the changeover to -eous is owed to some 16th-century wave of analogical refashionings that produced unetymological words like 'courteous' (for curteis < OF curteis < L -ēnsem), 'righteous' (for the phonological outcome of rightwise), etc.
<umunmutamku> So all we really need here is a plausible source of the root gid-, be it native English or French.
<umunmutamku> Luckily, we seem to have a good candidate in OE gidiʒ 'giddy', apparently etymologically *gudīgo- 'possessed by a god'. So we should be imagining a pretentious 16th-century refashioning to gideous, which, given the semantics of the word around that time, would have to mean 'intoxicated, vertiginous, insane'.
<tezcatlipoca> huzzah! You 'intoxicated, vertiginous, insane' prostitute!