Over-slender (5)
I believe the answer is:
spare
I believe this is a double definition.
'over' is the first definition.
(I've seen this before)
'slender' is the second definition.
(thesaurus)
(Other definitions for spare that I've seen before include "Thin; left over" , "Don't use" , "Not required" , "With no excess fat" , "In reserve; pardon" .)