The core idea of this root was:
grinding (something on a surface)
It’s the origin of the English word to grind and also of the German der Grind, which means scab (and you get it after you “ground open” your skin).
German etymological research speculates, that it’s the origin of der Grund and ground, based on the idea of coarse grains of a sandy ground.
I thought that maybe also words like grain and granular could then be related, but research doesn’t show any such connection.