alum

[ al-uhm ]

See synonyms for alum on Thesaurus.com

nounChemistry.

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.

Origin of alum

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 )

Other definitions for alum (2 of 3)

alum²

[ uh-luhm ]

nounInformal.

an alumna or alumnus: Nearly 45 of us alums went on a day trip on the river to celebrate graduation.

Origin of alum

First recorded in 1875–80; by shortening

usage note For alum

What's the difference between alum, alumnus, and alumna? See alumnus.

Words that may be confused with alum

alum , alumna, alumnae, alumni, alumnus

Other definitions for alum. (3 of 3)

alum.

abbreviationChemistry.

aluminum.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use alum in a sentence

A TNR alum dives deep in what happened with the 100-year-old institution.
The Daily Beast’s Best Longreads, Dec 8-14, 2014 | William Boot | December 13, 2014 | THE DAILY BEAST
And those who take issue with the ice bucket challenge have found an unexpected spokesperson in Jackass alum Steve-O.
#IceBucketChallenge Wisdom From 'Jackass' Steve-O | Kevin Zawacki | August 21, 2014 | THE DAILY BEAST
Marine friends, all ranks and all mostly Anbar fighting alum, have been sending me emails as well.
Their Fight…But Our Legacy: The New Battle for Fallujah | John Kael Weston | January 12, 2014 | THE DAILY BEAST
Apple alum Tony Fadell reinvented the boring market for home thermostats with his sleek and eco-savvy digital Nest.
How to Hack the Perfect Home | Daniel Gross | November 15, 2013 | THE DAILY BEAST
Petraeus, himself a Sosh alum, became the central figure for a mix of reasons.
The Petraeus Revolution: How He Changed the American Way of War | John Barry | January 8, 2013 | THE DAILY BEAST

If they require a second water put alum to that also as well as to the rinsing and blue water.
The Ladies' Book of Etiquette, and Manual of Politeness | Florence Hartley
Thus the proportions are omitted, and alum becomes alum compound, whatever that may mean.
The Propaganda for Reform in Proprietary Medicines, Vol. 1 of 2 | Various
On examination it was found that the enclosure of the Atarrea was broken down, and the source saturated with alum.
Travels in Peru, on the Coast, in the Sierra, Across the Cordilleras and the Andes, into the Primeval Forests | J. J. von Tschudi
The principal impurity, and one which renders alum unfit for the use of the dyer, is iron.
Cooley's Cyclopdia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades..., Sixth Edition, Volume I | Arnold Cooley
The applications of alum in the arts and manufactures are numerous and important.
Cooley's Cyclopdia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades..., Sixth Edition, Volume I | Arnold Cooley

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

Origin of 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

Scientific definitions for alum

alum

[ ăl′əm ]

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.

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