Nasty smell (5)
(Other definitions for odour that I've seen before include "Aroma, smell" , "Aroma or fragrance" , "Nasty smell" , "Smell, redolence" , "Olfactory sensation" .)
(Other definitions for hum that I've seen before include "Pong" , "Smell strongly" , "Sing with the mouth shut" , "Sound of a bee" , "Buzz; stink" .)