-ious

= -ous

Большой англо-русский словарь
-ious

adjective suffix Etymology: Middle English, partly from Anglo-French -ious, from Latin -iosus, from -i-, penultimate vowel of some noun stems + -osus -ous; partly from Latin -ius, adjective suffix -ous
Example: edacious

Merriam-Webster's Collegiate Dictionary