Also called potassium alum. Also called potash alum. a crystalline solid, aluminum potassium sulfate, K 2 SO 4 ⋅Al 2 (SO4 ) 3 ⋅24H 2 O, 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 R 2 SO 4 ⋅X 2 (SO4 ) 3 ⋅24H 2 O, where R is a univalent alkali metal or ammonium, and X one of a number of trivalent metals.
(not in technical use) aluminum sulfate.
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
What’s the difference between alum, alumnus, and alumni? The informal word alum refers to a graduate of a school, such as a high school or university. It’s a shortening of alumnus or alumna. In Latin, alumnus specifically refers to a male graduate, and sometimes this distinction is carried into English, with alumna being used to refer to a female graduate. The plural of alumna is alumnae. The plural of alumnus is alumni (which follows the plural ending construction used in other Latin-derived words, like stimulus and stimuli). Still, alumnus and alumni are both commonly used in a gender-neutral way. Alum is also used regardless of gender. It’s sometimes pluralized as alums. Here’s an example of alum and alumni used correctly in the same sentence. Example: As an alum, you share something with all of the alumni, regardless of when each of you graduated. Want to learn more? Read the breakdown of the difference between alumnus and alumni.
What's the difference between alum, alumnus, and alumna? See alumnus.
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 )
First recorded in 1875–80; by shortening
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
And ALUM, brave fellow, who stood in the fore,And never expected to look on them more,Was really delighted to see them again,For the truly courageous are truly humane.
From More Bab Ballads by Gilbert, W. S. (William Schwenck), Sir
For he knew, the brave ALUM, that, happen what might,With belts and cork-jacketing, he was all right;Though others might sink, he was certain to swim,—No Hareem whatever had terrors for him!
From More Bab Ballads by Gilbert, W. S. (William Schwenck), Sir
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
