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: K2SO4.Al2(SO4)3.24H2O
2.
any of a group of isomorphic double sulphates of a monovalent metal or group and a trivalent metal. Formula: X2SO4.Y2(SO4)3.24H2O, where X is monovalent and Y is trivalent
Word origin
C14: from Old French, from Latin alūmen
alum in British English2
(ˈæləm)
noun
informal, mainly US and Canadian
an alumnus or alumna
alum in American English1
(ˈæləm)
noun
1.
a double sulfate of a monovalent metal or radical (as sodium, potassium, or ammonium) with a trivalent metal (as aluminum, iron, or chromium): it is used as an astringent, as an emetic, and in the manufacture of baking powders, dyes, and paper: the commonest form is potash alum (potassium aluminum sulfate), KAl(SO4)2·12H2O
2.
aluminum sulfate: an erroneous use
Word origin
ME & OFr < L alumen, alum: for IE base see ale
alum in American English2
(əˈlʌm)
US
noun
Informal
an alumnus or alumna
alum in American English1
(ˈæləm)
noun Chemistry
1. 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
2.
one of a class of double sulfates analogous to the potassium alum, 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
3. (not in technical use)
aluminum sulfate
Word origin
[1275–1325; ME ‹ AF ‹ L alūmen; r. OE alefne, ælifnæ ‹ OWelsh (cf. MWelsh elyf) ‹ L alūmini- (s. of alūmen)]
alum in American English2
(əˈlʌm)
noun
informal
an alumna or alumnus
Word origin
[by shortening]
Examples of 'alum' in a sentence
alum
Why was the Duchess looking as though she had just swallowed a spoonful of powdered alum ?
Babson, Marian DEATH IN FASHION (1989)
In the bowl is a teaspoon of alum, for him to dip his finger into and touch onto the canker sore in his cheek.
Lordan, Beth AUGUST HEAT (1989)
All related terms of 'alum'
chrome alum
a violet-red crystalline substance, used as a mordant in dyeing . Formula: KCr(SO 4 ) 2 .12H 2 O
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
ammonium alum
Chemistry See aluminum ammonium sulfate
potassium alum
Chemistry alum 1 (sense 1 )
aluminum ammonium sulfate
a crystalline solid , AlNH 4 (SO 4 ) 2 ⋅12H 2 O, used chiefly as a size in the manufacture of paper; alum