alum
noun/ˈæləm/
/ˈæləm/
[uncountable]- a substance formed from aluminium and another metal, used, for example, to prepare leather and to change the colour of things
明矾，白矾（用于制革、印染等） Word Originlate Middle English: via Old French from Latin alumen, alumin- related to aluta ‘a kind of leather’.