hum (v.) Look up hum at
late 14c., hommen "make a murmuring sound to cover embarrassment," later hummen "to buzz, drone" (early 15c.), probably of imitative origin. Sense of "sing with closed lips" is first attested late 15c.; that of "be busy and active" is 1884, perhaps on analogy of a beehive. Related: Hummed.
hum (n.) Look up hum at
mid-15c., "a murmuring sound made with the voice," from hum (v.).