Where does “swi-” come from?

swi- (Proto-Indo-European) comes from Proto-Bantu jí-, from Navajo ní-, from Navajo ł-, from Proto-Athabaskan *-ɬ — Forms instrumental nouns from verbs.

Ancestry of “swi-”, step by step

Step	Language	Word	Meaning
1	Proto-Bantu	jí-	Class 10 pronominal concord; Class 10 subject...
2	Navajo	ní-	forms the comparative form of neuter imperfective verbs
3	Navajo	ł-	the
4	Proto-Athabaskan	*-ɬ	Forms instrumental nouns from verbs

Every word from Proto-Athabaskan *-ɬ →Every word from Navajo ní- →Every word from Proto-Bantu jí- →