Where does “*sa-” come from?

*sa- (Proto-Indo-Aryan) comes from Proto-Indo-Iranian sa-, from Proto-Indo-European sm̥-, from Proto-Indo-European sem- — together, one.

Ancestry of “*sa-”, step by step

StepLanguageWordMeaning
1Proto-Indo-Iraniansa-together, co-
2Proto-Indo-Europeansm̥-one; with, together
3Proto-Indo-Europeansem-together, one

Words derived from “*sa-”

Every word from Proto-Indo-European sem- →Every word from Proto-Indo-European sm̥- →Every word from Proto-Indo-Iranian sa- →