murmur (n.)youdaoicibaDictYouDict[murmur 词源字典]
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.[murmur etymology, murmur origin, 英语词源]
mutter (v.)youdaoicibaDictYouDict
early 14c., moteren "to mumble," from a common PIE imitative *mut- "to grunt, mutter" (cognates: Old Norse muðla "to murmur," Latin muttire "to mutter," Old High German mutilon "to murmur, mutter; to drizzle"), with frequentative suffix -er. Related: Muttered; muttering.
surd (adj.)youdaoicibaDictYouDict
1550s, "irrational" (of numbers), from Latin surdus "deaf, unheard, silent, dull; willfully deaf, inattentive," possibly related to susurrus "a muttering, whispering" (see susurration). The mathematical sense is from the use of Latin surdus to translate Arabic (jadhr) asamm "deaf (root)," itself apparently a loan-translation of Greek alogos, literally "speechless, without reason" (Euclid book x, Def.). In French, sourd remains the principal word for "deaf." As a noun from 1540s. Related: Surdity.
susurrus (n.)youdaoicibaDictYouDict
1809, earlier as a medical Latin word in English, from Latin susurrus, literally "a humming, muttering, whispering" (see susurration).
Among the diseases of the ear, one of the most prevalent is the Paracusis imaginaria, to which both sexes are equally liable; and another variety of the same tribe, more frequent among female patients, called the Susurrus criticus, or Scandal-buzz. ["The Lounger," Dec. 23, 1786]