mutterer

noun

1. One who mutters.

   “"To accuse a priest!" said someone in a tone of indignation, and a murmur arose at once in sympathy. ¶ It moved the young officer to mirth. He half-swung on his heel so as to confront those mutterers.”

   “c. 1954, Jack Kerouac, Untitled poem, in Book of Sketches, 1952-57, Penguin, 2006, p. 239, I, mutterer to / myself in childhood French […]”