I didn't catch that release (6)
I believe the answer is:
pardon
This clue is a double definition.
'i didn't catch that' is the first definition.
(both are said to ask someone to repeat something)
'release' is the second definition.
(pardon is a kind of release)
(Other definitions for pardon that I've seen before include "Excuse or absolve" , "Forgive (an error)" , "indulgence" , "Forgive or excuse (an offence)" , "Forgive - eh?" .)