alum

1
[ al-uhm ]
/ ˈæl əm /

noun Chemistry.

Also called potash alum, potassium alum. a crystalline solid, aluminum potassium sulfate, K2SO4⋅Al2(SO4)3⋅24H2O, used in medicine as an astringent and styptic, in dyeing and tanning, and in many technical processes.
one of a class of double sulfates analogous to aluminum potassium sulfate, as aluminum ammonium sulfate, having the general formula R2SO4⋅X2(SO4)3⋅24H2O, where R is a univalent alkali metal or ammonium, and X one of a number of trivalent metals.
(not in technical use) aluminum sulfate.

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Origin of alum

1
First recorded in 1275–1325; Middle English <Anglo-French, from Latin alūmen; replacing Old English alefne, ælifnæ, from Old Welsh (compare Medieval Welsh elyf ) <Latin alūmini- (stem of alūmen )

Definition for alum (2 of 3)

alum2
[ uh-luhm ]
/ əˈlʌm /

noun Informal.

an alumna or alumnus.

Origin of alum

2
by shortening

WORDS THAT MAY BE CONFUSED WITH alum

alum , alumna, alumnae, alumni, alumnus (see usage note at alumnus)

Definition for alum (3 of 3)

alum.

Chemistry.

aluminum.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Example sentences from the Web for alum

British Dictionary definitions for alum

alum
/ (ˈæləm) /

noun

Also called: potash alum a colourless soluble hydrated double sulphate of aluminium and potassium used in the manufacture of mordants and pigments, in dressing leather and sizing paper, and in medicine as a styptic and astringent. Formula: K 2 SO 4 .Al 2 (SO 4) 3 .24H 2 O
any of a group of isomorphic double sulphates of a monovalent metal or group and a trivalent metal. Formula: X 2 SO 4 .Y 2 (SO 4) 3 .24H 2 O, where X is monovalent and Y is trivalent

Word Origin for alum

C14: from Old French, from Latin alūmen
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for alum

alum
[ ăləm ]

n.

Any of various double sulfates of a trivalent metal such as aluminum or iron and a univalent metal such as potassium or sodium that are used as topical astringents and styptics.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for alum

alum
[ ăləm ]

Any of various crystalline double salts of a trivalent metal (such as aluminum, chromium, or iron) and a monovalent metal (such as potassium or sodium), especially aluminum potassium sulfate. Alum is widely used in industry as a hardener and purifier, and in medicine as an emetic and to stop bleeding.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.