Pardon sailor on crack (7)
I believe the answer is:
absolve
'pardon' is the definition.
(I've seen this before)
'sailor on crack' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'on' means one lot of letters go next to another.
'crack' becomes 'solve' (I've seen this before).
'ab'+'solve'='ABSOLVE'
(Other definitions for absolve that I've seen before include "Declare to be free from blame" , "Let off the hook" , "Declare (someone) blameless" , "Forgive sins" , "Free (a person) from guilt" .)