"be silent," 1560s, from a verb mum (Middle English mommen) "make silent" (c. 1400); "be silent" (mid-15c.), from mum, mom (late 14c.), "an inarticulate closed-mouth sound" indicative of unwillingness or inability to speak, probably imitative. As an adjective meaning "secret" or "silent" from 1520s. Phrase mum's the word is recorded by 1704.

1580s, "complain in a low voice;" 1590s, "make a low, rumbling sound," from French grommeler "mutter between the teeth" or directly from Middle Dutch grommelen "murmur, mutter, grunt," from grommen "to rumble, growl." Imitative, or perhaps akin to grim (adj.). With unetymological -b- as in mumble. Related: Grumbled; grumbling.

boys' knife-throwing game, 1650s, originally mumble-the-peg (1620s), of unknown signification and origin. The usual story is that it is so called because "The last player to complete the series is compelled to draw out of the ground with his teeth a peg which the others have driven in with a certain number of blows with the handle of the knife" [Century Dictionary]; see mumble (v.) in the original sense "eat in a slow, inefficient manner."

type of contagious disease characterized by inflammation of the glands, c. 1600, from plural of mump "a grimace" (1590s), originally a verb, "to whine or mutter like a beggar" (1580s), from Dutch mompen "to cheat, deceive," originally probably "to mumble, whine" and of imitative origin (compare mum (interj.), mumble). The infectious disease probably was so called in reference to swelling of the salivary glands of the face and/or to painful difficulty swallowing. Mumps also was used from 17c. to mean "a fit of melancholy, sullenness, silent displeasure."