Say Hillary Clinton, initially flexible (7)
I believe the answer is:
climber
'say hillary' is the definition.
(I know that Edmund Hillary is a mountain climber)
'clinton initially flexible' is the wordplay.
'initially' indicates taking the first letters.
'flexible' becomes 'limber' (similar in meaning).
The first letter of 'clinton' is 'c'.
'c'+'limber'='CLIMBER'
(Other definitions for climber that I've seen before include "Mountaineer" , "Plant that grows up a support" , "Bonnington" , "Edward Whymper, for example" , "Plant such as ivy" .)