Up-tempo shindig? (4,4)
I believe the answer is:
high time
'shindig?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'up-tempo' is the wordplay.
'up' becomes 'high' (associated in meaning).
'tempo' becomes 'time' (I've seen this before).
'high'+'time'='HIGH TIME'
Can you help me to learn more?
(Other definitions for high time that I've seen before include "long overdue" , "'The latest possible moment (4,4)'" , "Beyond the proper hour, but not too late - check lofty clock" .)