Cilla's blossoming form (5)

I believe the answer is:

lilac

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'blossoming form' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'cilla's' is the wordplay.
'cilla' anagrams to 'LILAC'.
However, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for lilac that I've seen before include "Pale purple - flowering tree" , "Purplish in colour" , "Shade" , "Pale pinkish-violet" , "Flower celebrated by Schubert" .)

I've seen this clue in the Evening Standard.

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