bellow

Origin

From Middle English belwen, from Old English belgan, bylgan (“to become angry, to swell with rage”), ultimately from the Proto-Indo-European *bʰel- (“to sound, roar”), whence also belg (“leather bag”), bellan (“to roar”), blāwan (“to blow”). Cognate with German bellen (“to bark”), Russian бле́ять (bléjatʹ, “baa, bleat”). Compare billow (“wave”), of the same root, also bulge, with related etymology to swelling. Potentially related to bawl, Swedish böl (“bawl”).