Backless footwear (4)
I believe the answer is:
mule
'backless footwear' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mule that I've seen before include "The animal said to be stubborn" , "Sterile offspring of donkey and horse" , "Offspring of a donkey and a mare" , "Obstinate quadruped" , "Hybrid beast" .)