An Etymological Dictionary of the German Language/Annotated/brüllen

by Friedrich Kluge

brüllen, verb, ‘to roar, bellow, low,’ from the equivalent Middle High German brüelen; in Upper German dialects even now briele, brüele. The remarkable short ü of Modern High German compared with Middle High German üe may be explained by the preterite brülte, where the shortness of the vowel is produced by the following double consonant; Old High German *bruowilôn is wanting; allied perhaps to English brawl?. From the root brô (‘to scald’) in the sense of ‘to bubble’?.