Grad at a reunion (4)

I believe the answer is:

alum

(Other definitions for alum that I've seen before include "Compound used in tanning and dying" , "Name given to a specific chemical compound and a class of them" , "Aluminium/potassium sulphate" , "Sulphate used in dyeing and tanning" , "White mineral salt used in medicine and in dyeing" .)

I've seen this clue in the Newsday and the Newsday.com.

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