Alum

al′um, n. a mineral salt, the double sulphate of alumina and potash, used as a mordant in dyeing and for many purposes.— adj. Al′umish , having the character or taste of alum.— ns. Al′um-shale , or -slate , a slate consisting mainly of clay, iron pyrites, and coaly matter, from which alum is obtained. [L. alumen .]