Sacked or let off (5)
I believe the answer is:
fired
'sacked' is the definition.
(both can mean dismissed from a job)
'let off' is the wordplay.
I cannot really see how this works, but
'let off' could be 'fire' (I've seen this before) and 'fire' is found in the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
'or' is the link.
Can you help me to learn more?
(Other definitions for fired that I've seen before include "Encouraged" , "sent up in flames" , "Dismissed; set off" , "Stimulated; dismissed" , "Set ablaze" .)