Prison is no different from a boarding house (7)
I believe the answer is:
pension
'a boarding house' is the definition.
(I've seen this before)
'prison is no different' is the wordplay.
'prison' becomes 'pen' (both can mean an enclosure).
'different' indicates an anagram (letters placed in a different order).
'is'+'no'='isno'
'isno' is an anagram of 'sion'.
'pen'+'sion'='PENSION'
'from' acts as a link.
(Other definitions for pension that I've seen before include "Retiree's income" , "Income in retirement" , "Regular payment for older people" , "Payment to traitor" , "Regular payment for retired persons" .)