Face struggle to conceal droop (6)
I believe the answer is:
visage
'face' is the definition.
(visage is a kind of face)
'struggle to conceal droop' is the wordplay.
'struggle' becomes 'vie' (I've seen this before).
'to conceal' is an insertion indicator.
'droop' becomes 'sag' ('sag' can be a synonym of 'droop').
'vie' placed around 'sag' is 'VISAGE'.
(Other definitions for visage that I've seen before include "Mug" , "A person's face, countenance" , "Face, aspect" , "Clock" .)