Universal wit entertaining third of listeners (6)

I believe the answer is:

cosmic

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'universal' is the definition.
(relating to the universe)

I can't explain the rest of the clue.

(Other definitions for cosmic that I've seen before include "Enormous" , "Relating to the universe" , "Great" , "Significant" , "To do with the whole universe" .)

I've seen this clue in The Times.

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