Where does “grienen” come from?

grienen (Low German) comes from Middle Low German grînen, from Old Saxon grīnan, from Proto-Germanic *grīnan.

Ancestry of “grienen”, step by step

Step	Language	Word	Meaning
1	Middle Low German	grînen	—
2	Old Saxon	grīnan	—
3	Proto-Germanic	*grīnan	—

grienen — Etymology, Origin & Word History | Etymology Explorer