Pleasant occasion after engineers withdraw (7)
I believe the answer is:
retreat
'withdraw' is the definition.
(I know that withdraw can be written as retreat)
'pleasant occasion after engineers' is the wordplay.
'pleasant occasion' becomes 'treat' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' is a charade indicator (letters next to each other).
'engineers' becomes 're' (Royal Engineers).
'treat' after 're' is 'RETREAT'.
Can you help me to learn more?
(Other definitions for retreat that I've seen before include "retirement" , "Monastery - bugle call" , "It may be secluded" , "hermitage, perhaps" , "Back away" .)