Green’s Dictionary of Slang

an unpleasant smell.

1719		in D’Urfey Pills to Purge Melancholy I 28: The fart; Famous for its Satyrical Humour in the Reign of Queen anne: [...] They both from one Bottom did come, / The one thin and lean, / As a Garden French Bean, / And tother as round as a Drum; / With a hum, hum, hum, hum.
1906		E. Dyson Fact’ry ’Ands 197: That knowledge groaned all over ther factory, ther hum iv it was so fearful.
1910		Bulletin (Sydney) 27 Oct. 14/1: You could smell Nosey coming. [...] ‘It ain’t that,’ said the patient, ‘it’s the -- hum that hurts.’.
1914		E. Dyson Spats’ Fact’ry (1922) 75: Ev’ry one else got’ardened t’ th’ hum iv onyins, but Artie he never cud.
1939		‘Flann O’Brien’ At Swim-Two-Birds 63: There’s a hum off yourself, I said.
1940		M. Marples Public School Slang 160: SMELL. Some forceful synonym is generally preferred to the simple word — e.g. hum, niff (adj. niffy), pong, stink, whiff [ad], whiffy).
1969		P. Boyle All Looks Yellow to the Jaundiced Eye 51: There’s a hum rising, thick as a cloud of midges, that only cigarette smoke would disperse.
1991		R. Doyle Van (1998) 401: I’m tellin’ yeh, compadre, the hum is fuckin’ atrocious.
2005		P. Howard Curious Incident of the Dog in the Nightdress 123: Hell of a hum off him, isn’t there?