From Proto-Indo-European *mormur-, *mur- (“to mutter”). Reduplication points to imitative, onomatopoeic origin of the root. Cognate with Sanskrit मर्मर (marmara, “rustling sound, murmur”), Ancient Greek μορμύρω (mormúrō, “to roar, boil”), Lithuanian mùrmėti (“to mutter, murmur, babble”), Old High German murmurōn, murmulōn (“to mumble, murmur”), Old Norse murra (“to grumble, mumble”), Old Armenian մռմռամ (mṙmṙam).