late 14c., "expression of discontent by grumbling," from Old French murmure "murmur, sound of human voices; trouble, argument" (12c.), noun of action from murmurer "to murmur," from Latin murmurare "to murmur, mutter," from murmur (n.) "a hum, muttering, rushing," probably from a PIE reduplicative base *mor-mor, of imitative origin (cognates: Sanskrit murmurah "crackling fire," Greek mormyrein "to roar, boil," Lithuanian murmlenti "to murmur"). Meaning "softly spoken words" is from 1670s.
