For a celebrity, a drop of Scotch serves as a stiffener (6)

I believe the answer is:

starch

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'stiffener' is the definition.
(starch is used to make fabric stiff)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for starch that I've seen before include "foodstuff" , "ceremony" , "rigid" , "Formality - give stiffness" , "Formality - makes things stiff" .)

I've seen this clue in the Evening Standard.

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