Missing the first celebration of summer? (7)

I believe the answer is:

estival

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'of summer?' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for estival that I've seen before include "No following for joyful celebration" , "summer in the States" , "occurring in Washington summer?" .)

I've seen this clue in The Hindu.

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