köken: A Low and Central German word, attested in High German texts from the 15th century. From northern Middle High German *klumpe and Middle Low German klumpe, both from Old Saxon *klumpo, from Proto-Germanic *klumpô (“mass, lump, clump; clasp”), from Proto-Indo-European *glembʰ- (“lump, clamp”). Cognate with Dutch klomp (whence English clump), Danish klump, Swedish klump.
köken: According to Bulgarian Etymological Dictionary, probably from буте́я (butéja, “to swell, to clumb”) (dialectal) + -ца (-ca) (formally reflecting an earlier *butьca).