Flexible concerning one in movie (9)
I believe the answer is:
resilient
'flexible' is the definition.
(I've seen this before)
'concerning one in movie' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'movie' becomes 'silent' (silent movie is a kind of movie).
'i' put inside 'silent' is 'silient'.
're'+'silient'='RESILIENT'
(Other definitions for resilient that I've seen before include "Able to spring back into shape" , "Rebounding from impact" , "Able to recover quickly" , "bouncing back" , "Elastic" .)