Expresses surprise in funny afterthought (5)
I believe the answer is:
gasps
'expresses' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Perhaps you can see a link between them that I don't see?
'surprise in funny afterthought' is the wordplay.
'surprise in funny' becomes 'gas' (I can't explain this - if you can you should believe this answer much more).
'afterthought' becomes 'ps' (as in a PS in a letter).
'gas'+'ps'='GASPS'
Can you help me to learn more?
(Other definitions for gasps that I've seen before include "'Pants, puffs (5)'" , "Draws breath sharply" .)