An Etymological Dictionary of the German Language/Annotated/Grat
Grat, masculine, and Gräte, feminine, ‘point, ridge, fish-bone,’ from Middle High German grât, masculine, ‘fish-bone, awn, back-bone, mountain ridge’; in Modern High German the word has assumed two forms, according to the meanings. Since Graune, ‘awn,’ has also the dialectic sense ‘fish-bone,’ both words may perhaps be traced back to a common root gra-, ‘to be pointed, bristly.’