Where does “grot” come from?

grot (Luxembourgish) comes from Luxembourgish gro, from Old High German grāo, from Proto-Germanic grēwaz, from Proto-Indo-European ǵʰreh₁- — to become green, grow; to grow; to green, to grow.

grot (Luxembourgish): neuter nominative of gro; neuter accusative of...