One that can be let off employment after sack (8)
I believe the answer is:
firework
'one that can be let' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'employment after sack' is the wordplay.
'employment' becomes 'work' (synonyms).
'after' means one lot of letters go next to another.
'sack' becomes 'fire' (both can mean to dismiss from a job).
'work' after 'fire' is 'FIREWORK'.
'off' is the link.
Can you help me to learn more?
(Other definitions for firework that I've seen before include "rocket" , "fountain, say" , "Banger, for example" , "Pyrotechnic device" , "Colourful incendiary device used for entertainment" .)