Where does “sublum” come from?

sublum (Vulgar Latin) comes from Latin sūbulum, from Latin insubulum, from Latin insuō, from Latin īn-, from Latin în, from Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

Ancestry of “sublum”, step by step

Step	Language	Word	Meaning
1	Latin	sūbulum	—
2	Latin	insubulum	warp beam of a weaver's loom
3	Latin	insuō	to sew up; to sew in or into
4	Latin	īn-	un-, non-, not
5	Latin	în	in, at, on, upon, from (space)
6	Latin	en	lookǃ beholdǃ; reallyǃ?; come onǃ
7	Proto-Italic	en	in
8	Proto-Indo-European	h₁én	in

Words derived from “sublum”

subbio
sul
insubbiare

Every word from Proto-Indo-European h₁én →Every word from Latin īn- →Every word from Proto-Italic en →