A zip's caught — whoopee! (6)
I believe the answer is:
hurray
'whoopee' is the definition.
(both are joyful exclamations)
'a zip's caught' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'zip' could be 'hurry' (synonyms) and 'hurry' is found within the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hurray that I've seen before include "very brief message of joy" , "cheer" , "Yippee!" .)