Nice chap put back son's departure (6)
I believe the answer is:
egress
'departure' is the definition.
(I've seen this before)
'nice chap put back son's' is the wordplay.
I cannot really see how this works, but
'son's' could be 'ss' (genealogical abbreviation for son) and 'ss' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for egress that I've seen before include "Emergence - exit" , "Emergence, coming out" , "The act of leaving a building" , "Act of exiting" , "Taking leave" .)