Where does “combrous” come from?

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

Ancestry of “combrous”, step by step

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