Flexible creeper pruned in part (6)
I believe the answer is:
pliant
'flexible' is the definition.
('pliant' can be a synonym of 'flexible')
'creeper pruned in part' is the wordplay.
'creeper' becomes 'liana' (creeping plant).
'pruned' means to remove the last letter.
'in' indicates putting letters inside.
'part' becomes 'pt' (I've seen this in other clues**).
'liana' with its final letter taken away is 'lian'.
'lian' put inside 'pt' is 'PLIANT'.
(Other definitions for pliant that I've seen before include "easily modified" , "Flexible - yielding" , "Not firm" , "Accommodating" , "Plastic" .)