Where does “грм” come from?

грм (Serbo-Croatian) comes from Proto-Slavic grъmъ, from Proto-Slavic grъdmъ, from Proto-Slavic gruditi, from Proto-Balto-Slavic groud-.

грм (Serbo-Croatian): bush

Definitions

Step	Language	Word	Meaning
1	Proto-Slavic	grъmъ	bush, shrub
2	Proto-Slavic	grъdmъ	—
3	Proto-Slavic	gruditi
4	Proto-Balto-Slavic	groud-	—

грм — Etymology, Origin & Word History | Etymology Explorer