Where does “sober” come from?

sober (Middle English) comes from Old French sobre, from Latin sōbrius, from Latin sē-, from Latin sex, from Proto-Italic seks, from Proto-Indo-European swéḱs — six.

Ancestry of “sober”, step by step

Step	Language	Word	Meaning
1	Old French	sobre	—
2	Latin	sōbrius	—
3	Latin	sē-	—
4	Latin	sex	six; 6
5	Proto-Italic	seks	six
6	Proto-Indo-European	swéḱs	six

Every word from Proto-Indo-European swéḱs →

sober — Etymology, Origin & Word History | Etymology Explorer