Where does “Струма” come from?

Струма (Bulgarian) comes from Ancient Greek Στρυμών, from Proto-Indo-European sréw-mō, from Proto-Indo-European srew-, from Proto-Indo-European ser- — to flow; to guard; to bind, to tie together.

Ancestry of “Струма”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Στρυμών	Strymon
2	Proto-Indo-European	sréw-mō	—
3	Proto-Indo-European	srew-	to flow, stream
4	Proto-Indo-European	ser-	to flow; to guard; to bind, to tie together

Words derived from “Струма”

strumous
struma
strumiferous
strumectomy
strumiform
strumitis
strumosis
antistrumous
strumousness
strumously

Every word from Proto-Indo-European ser- →Every word from Proto-Indo-European srew- →Every word from Proto-Indo-European sréw-mō →