Grellmann (1787) collected the following names for various types of horses of which the above seem to be a development: Gra, Grea, Krej ‘a horse’; Gratsch, Grast ‘a Stallion’; Grasni, Gaschni ‘a Mare’ from Continental gipsies.
Smart & Crofton (1875) collected the form Grei., n., ‘a horse’ from English Gypsies.
Canadian Paul Pope (2013) cites the form gry ‘a horse’.