For a celebrity, a drop of Scotch serves as a stiffener (6)
I believe the answer is:
starch
'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" .)