Where does “grom” come from?

grom (Old English) comes from Proto-Germanic gramaz, from Proto-Indo-European gʰrem-, from Proto-Indo-European gʰer- — to rub; to stroke; to grind.

Ancestry of “grom”, step by step

Step	Language	Word	Meaning
1	Proto-Germanic	gramaz	furious; hostile
2	Proto-Indo-European	gʰrem-	to be angry; to sound, bellow, growl, roar, be...
3	Proto-Indo-European	gʰer-	to rub; to stroke; to grind

grom — Etymology, Origin & Word History | Etymology Explorer