There are 2 main definitions of alum in English:

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alum 1

Pronunciation: /ˈaləm/

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. Also called potash alum.
  • Chemical formula: AlK(SO4)2.12H2O
Example sentences
  • It could also be treated by rubbing salt, brain or potash alum into the surface to produce a very pale leather.
  • Astringent varieties contain alum, which makes your mouth pucker when the fruits are eaten before they're fully ripe.
  • I have no idea how it's manufactured, but it's a kind of alum, a double sulfate of aluminum in crystal salt form.
1.1Any of a number of analogous crystalline double sulfates of a monovalent metal (or group) and a trivalent metal.
Example sentences
  • 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'.

Words that rhyme with alum

Calum, mallam, vallum
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There are 2 main definitions of alum in English:

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alum 2

Pronunciation: /əˈləm/

noun

informal, chiefly US

Origin

Late 19th century: abbreviation.

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