Where does “sumr” come from?

sumr (Old Norse) comes from Proto-Germanic sumaz, from Proto-Indo-European sem- — together, one.

sumr (Old Norse): some

Definitions

Step	Language	Word	Meaning
1	Proto-Germanic	sumaz	some , a certain; some, certain
2	Proto-Indo-European	sem-	together, one

sumr — Etymology, Origin & Word History | Etymology Explorer