Jail in which you'd chill out (6)
I believe the answer is:
cooler
'jail in which you'd' is the definition.
'cooler' can be an answer for 'jail' (thesaurus). I'm not sure about the rest of the definition.
'chill out' is the wordplay.
'chill' becomes 'cool' (synonyms).
'out' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'cool'+'er'='COOLER'
Can you help me to learn more?
(Other definitions for cooler that I've seen before include "Nick" , "more sophisticated" , "Fan" , "It's not so hot" , "Prison - less warm" .)