Let out of jail, finally relax (5)
I believe the answer is:
lease
'let' is the definition.
('lease' can be a synonym of 'let')
'jail finally relax' is the wordplay.
'finally' suggests the final letters.
'relax' becomes 'ease' (I've seen this before).
The last letter of 'jail' is 'l'.
'l'+'ease'='LEASE'
'out of' is the link.
(Other definitions for lease that I've seen before include "Let out, hire" , "Tenancy contract" , "Tenancy agreement" , "Contract for use of land or building" , "Charter" .)