Main definitions of alum in English

: alum1alum2

alum1

noun

Chemistry
  • 1A colorless astringent compound that is a hydrated double sulfate of aluminum and potassium, used in solution medicinally and in dyeing and tanning.

    • ‘Astringent varieties contain alum, which makes your mouth pucker when the fruits are eaten before they're fully ripe.’
    • ‘One site said that clarifying agents could control snails, so I sent my son to the chemist for alum.’
    • ‘It could also be treated by rubbing salt, brain or potash alum into the surface to produce a very pale leather.’
    • ‘This, washed and then boiled, yielded aluminium sulphate, which, when ammonia was added, became alum.’
    • ‘I have no idea how it's manufactured, but it's a kind of alum, a double sulfate of aluminum in crystal salt form.’
    1. 1.1Any of a number of analogous crystalline double sulfates of a monovalent metal (or group) and a trivalent metal.
      • ‘Several decades later the Englishman Davy attempted to obtain the metal hidden in alums.’
      • ‘Aluminium dross tailings were used to produce two types of alums.’

Origin

Late Middle English: via Old French from Latin alumen, alumin-; related to aluta tawed leather.

Main definitions of alum in English

: alum1alum2

alum2

noun

US
informal
  • An alumnus or alumna.

    ‘a fellow Wellesley alum’

Origin

Late 19th century: abbreviation.