Where does “трс” come from?

трс (Serbo-Croatian) comes from Proto-Slavic tьrsъ, from Latin tirsus, from Ancient Greek Θύρσος.

Ancestry of “трс”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	tьrsъ	—
2	Latin	tirsus	—
3	Ancient Greek	Θύρσος	—

трс — Etymology, Origin & Word History | Etymology Explorer