On the move from a prison (5)
I believe the answer is:
astir
'on the move' is the definition.
(I've seen this in another clue)
'a prison' is the wordplay.
'prison' becomes 'stir' (informal term for prison).
'a'+'stir'='ASTIR'
'from' is the link.
(Other definitions for astir that I've seen before include "Starting to move" , "Up and about -- is art (anag)" , "abroad" , "In a state of movement" , "Moving; out of bed" .)