-eous · suffix1
From earlier -uous, alteration of -wose, -wos, a variant of -wise, from Middle English -wise, -wis, -wys, from Old English -wīs (“-wise”), under the influence of Etymology 2. More at -wise.
-eous · suffix2
Chiefly from -ous with preceding vowel (compare -ious); compare also Latin -eus; but also by concatenation with English -te (an earlier form of -ty).
Etymology from Wiktionary, CC BY-SA 4.0.