Class reunion attendee, for short (4)

I believe the answer is:

alum

(Other definitions for alum that I've seen before include "Sulphate; maul (anag.)" , "Compound used in tanning and dying" , "White mineral salt used in medicine and in dyeing" , "Sulphate used in dyeing and tanning" , "Aluminium/potassium sulphate" .)

I've seen this clue in the Wall Street Journal and the Universal.

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