Prisoner has endless space to dance (5)
I believe the answer is:
conga
'dance' is the definition.
(congaing is a kind of dancing)
'prisoner has endless space' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'has' says to put letters next to each other.
'endless' means to remove the last letter.
'space' becomes 'gap' (gap is a kind of space).
'gap' with its final letter removed is 'ga'.
'con'+'ga'='CONGA'
'to' acts as a link.
(Other definitions for conga that I've seen before include "Circuitous line dance" , "Line-dancing" , "Dance performed in line" , "Serpentine dance" , "Latin American dance with three steps and a kick" .)