Skit’s ending with harebrained nonsense (5)
I believe the answer is:
trash
'nonsense' is the definition.
(I know that nonsense can be written as trash)
'skit's ending with harebrained' is the wordplay.
'ending' indicates one should take the final letters (the ending of the word).
'with' is a charade indicator (letters next to each other).
'harebrained' becomes 'rash' (both can mean senseless or silly).
The final letter of 'skit' is 't'.
't'+'rash'='TRASH'
(Other definitions for trash that I've seen before include "Rubbish - destroy" , "Garbage or nonsense" , "bunk" , "Refuse, waste" , "Worthless people; destroy (US slang)" .)