All rest is spasmodic for the stars (7)

I believe the answer is:

stellar

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

'spasmodic for the stars' is the definition.
I can't judge whether this definition defines the answer.

'all rest' is the wordplay.
'all rest' can be anagrammed to 'STELLAR'.
But, I'm unsure how the anagram is indicated.

'is' acts as a link.

Can you help me to learn more?

(Other definitions for stellar that I've seen before include "Like highlights" , "Relating to the stars" , "Astral" , "Starry" , "like a star" .)

I've seen this clue in The Globe and Mail.

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