Many a donor, for short (4)

I believe the answer is:

alum

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

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.