An Etymological Dictionary of the German Language/grob
grob, adj., ‘coarse, uncouth, rude,’ from MidHG. grop(b), gerop, OHG. gerob, grob, ‘thick, awkward, indelicate’; comp. Du. and MidLG. grof, ‘coarse.’ The explanation of the word is not certain, since it is wanting in the other Teut. languages; it is undecided whether the term is compounded with ge-, Goth. ga-; if Goth. *ga-hruba- were the primit. form, the connection with AS. hreóf, OHG. riob, ‘scabiosus,’ would still remain doubtful.