Where does “vanadous” come from?

vanadous (English) comes from English -ous, from Middle English -ous, from Old French -us, from Latin -ōsus, from Old Latin -ōssus.

vanadous (English): Of, pertaining to or containing vanadium,...

Definitions

Step	Language	Word	Meaning
1	English	-ous	Used to form adjectives from nouns, to denote...
2	Middle English	-ous	—
3	Old French	-us	-ous, used for forming adjectives
4	Latin	-ōsus	ose, -ous, -ful (full of or overly prone to)
5	Old Latin	-ōssus	—