Where does “autumnal” come from?

autumnal (Old French) comes from Latin autumnālis, from Latin autumnus, from Latin auctumnus, from Proto-Indo-European h₃ewǵ- — cold.

autumnal (Old French): autumnal

Definitions

Step	Language	Word	Meaning
1	Latin	autumnālis	—
2	Latin	autumnus	autumn, fall; autumn; autumnal
3	Latin	auctumnus	autumn; autumn; autumnal
4	Proto-Indo-European	h₃ewǵ-	cold

autumnal — Etymology, Origin & Word History | Etymology Explorer