Classmates.com user (4)
I believe the answer is:
alum
(Other definitions for alum that I've seen before include "Name given to a specific chemical compound and a class of them" , "White mineral salt used in medicine and in dyeing" , "Sulphate used in dyeing and tanning" , "Compound used in dyeing and to stop bleeding" , "Potassium compound; IoW sandy bay" .)