Gloomy person cut hair (3)
I believe the answer is:
mop
'hair' is the definition.
(mop can mean a mass of hair)
'gloomy person cut' is the wordplay.
'gloomy person' becomes 'mope' (mope can mean a miserable person).
'cut' means to remove the last letter.
'mope' with its last letter removed is 'MOP'.
(Other definitions for mop that I've seen before include "Swab" , "Finish off a task - . . . up" , "Mass of disordered hair" , "Floor wiper" , "Implement for washing floor" .)