Excellent! McCartney's being broadcast (7)

I believe the answer is:

stellar

I'm a little stuck... Click here to teach me more about this clue!

'excellent' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for stellar that I've seen before include "Top-notch" , "characteristic of The Sun, etc" , "of celebrities" , "Outstanding -- star-like" , "Star-like, with star quality" .)

I've seen this clue in The Guardian.

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