Alum

Alum is both a specific chemical compound and a class of chemical compounds.
Examples:
History.
Words like "alum" and "potash" were used before modern chemistry developed. The word 'alumen' occurs in Pliny's "Natural History" (2379 AD). In the 52nd chapter of his 35th book, he gives a detailed description. Different substances were distinguished by the name of 'alumen', but they were all astringents, and were all used in dyeing and medicine.