Lithe, flexible (6)
I believe the answer is:
lissom
I believe this clue is a double definition.
'lithe' is the first definition.
(I know that lithe can be written as lissom)
'flexible' is the second definition.
(I've seen this before)
(Other definitions for lissom that I've seen before include "Limber" , "Agile and lithe" , "Lithe and flexible" , "Supple, nimble" , "Supple or agile" .)