alum

• POS: Noun

CIDE DICTIONARY

alum, n. [OE. alum, alom, OF. alum, F. alun, fr. L. alumen alum.].

 A double sulphate formed of aluminium and some other element (esp. an alkali metal) or of aluminium. It has twenty-four molecules of water of crystallization.  [1913 Webster]
" Common alum is the double sulphate of aluminium and potassium. It is white, transparent, very astringent, and crystallizes easily in octahedrons. The term is extended so as to include other double sulphates similar to alum in formula."  [1913 Webster]

alum, v. t. 

 To steep in, or otherwise impregnate with, a solution of alum; to treat with alum.  Ure.  [1913 Webster]

OXFORD DICTIONARY

alum, n.
1 a double sulphate of aluminium and potassium.
2 any of a group of compounds of double sulphates of a monovalent metal (or group) and a trivalent metal.

Etymology

ME f. OF f. L alumen aluminis

ROGET THESAURUS

alum

Sourness

N sourness, acid, acidity, low pH, acetous fermentation, lactic fermentation, vinegar, verjuice, crab, alum, acetic acid, lactic acid, sour, acid, acidulous, acidulated, tart, crabbed, acetous, acetose, acerb, acetic, sour as vinegar, sourish, acescent, subacid, styptic, hard, rough, sour as a lemon, (4) Odor.