Unfinished display behind is low (3)
I believe the answer is:
moo
'low' is the definition.
(both can mean to make a cow noise)
'unfinished display behind' is the wordplay.
'unfinished' means to remove the last letter.
'display behind' becomes 'moon' (moon can mean to show one's bottom).
'moon' with its last letter removed is 'MOO'.
'is' acts as a link.
(Other definitions for moo that I've seen before include "Guernsey noise?" , "Farmyard sound" , "Cow's sound" , "Cow's call" , "Irritating woman" .)