Unable to keep still (7)
I believe the answer is:
restive
'unable to keep still' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for restive that I've seen before include "Unsettled" , "Fidgety, uneasy" , "Unable to keep still" , "Impatient of authority" , "Impatient - jumpy" .)