Meaning of ALUM in English

I. ˈaləm noun

( -s )

Etymology: Middle English, from Middle French alum, alun, from Latin alumen — more at ale

1. : either of two colorless or white isomorphous crystalline double sulfates of aluminum having a sweetish-sourish astringent taste used chiefly in medicine internally as emetics and locally as astringents and styptics:

a. : the potassium double sulfate KAl(SO 4 ) 2 .12H 2 O occurring naturally and also made commercially (as by treating bauxite with sulfuric acid and then potassium sulfate) : potassium aluminum sulfate — called also potash alum, potassium alum ; compare alunite , kalinite

b. : the ammonium double sulfate NH 4 Al(SO 4 ) 2 .12H 2 O made commercially (as from ammonium sulfate and aluminum sulfate) — called also ammonia alum, ammonium alum

2. : any of a series of double salts isomorphous with potash alum that may contain analogous elements in place of the potassium, aluminum, and sulfur

soda alum

chrome alum

selenium alum

— compare pseudoalum

3. : aluminum sulfate — used chiefly commercially

II. əˈləm noun

( -s )

Etymology: by shortening

: an alumnus or alumna

Webster's New International English Dictionary.      Новый международный словарь английского языка Webster.