Where does “ample” come from?

ample (Middle French) comes from Old French ample, from Latin amplus, from Latin -ō, from Proto-Indo-European -ō — Derives nouns from roots.

Ancestry of “ample”, step by step

Step	Language	Word	Meaning
1	Old French	ample	—
2	Latin	amplus	large, spacious, roomy; abundant, ample;...
3	Latin	-ō	suffixed to nouns or adjectives. Originally a-stem nouns. Later extended to nouns with other stems. Forms regular first-conjugation verbs
4	Proto-Indo-European	-ō	Derives nouns from roots