Who’s an introvert — Viole.. Viol...Vio ...? (9,6)

I believe the answer is:

shrinking violet

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'who's' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for shrinking violet that I've seen before include "shy type" , "Exaggeratedly shy person" , "Person not likely to stand out" , "wallflower" , "Plant not growing" .)

I've seen this clue in The Hindu.

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