Extend a prison term (7)
I believe the answer is:
stretch
I believe this is a double definition.
'extend' is the first definition.
(I know that extend can be written as stretch)
'a prison term' is the second definition.
(I've seen this in another clue)
(Other definitions for stretch that I've seen before include "extended" , "Spell of time (in prison?)" , "Tax" , "Pull to make longer or wider" , "Make demands on; lengthen" .)