Hum original piece of Mahler in market (5)
I believe the answer is:
smell
'hum' is the definition.
(I've seen this before)
'original piece of mahler in market' is the wordplay.
'original piece of' indicates taking the first letters.
'in' indicates putting letters inside.
'market' becomes 'sell' (I've seen this in another clue).
The first letter of 'mahler' is 'm'.
'm' going within 'sell' is 'SMELL'.
(Other definitions for smell that I've seen before include "Scent" , "Sniff" , "Perceive through the nose" , "Hum" , "Aroma" .)