Again let loose (7)
I believe the answer is:
release
'loose' is the definition.
(loose can mean to untie or release)
'again let' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'let' becomes 'lease' (as in to lease or let a building).
're'+'lease'='RELEASE'
(Other definitions for release that I've seen before include "Prisoner eagerly awaits this" , "loose" , "Let go" , "put out" , "Set free - publish" .)