A number pointlessly parched (6)
I believe the answer is:
'a number' is the definition.
(thirty is a kind of number)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for thirty that I've seen before include "Six times five" , "November's days" , "Days in September, April, June and November" , "Half of threescore" , "Number of across clues in this puzzle" .)