alum

Etymology 1

From Middle English alum, alum, alym, alyme, from Anglo-Norman alum, alun, from Latin alūmen.

noun

1. An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and aluminium (K₂SO₄·Al₂(SO₄)₃·24H₂O).
   Venice also needed alum for trade, since it was the point of departure for overland transportation of alum to southern Germany and its cloth-manufacturing Free Cities. 1991, Felix Gilbert, The Pope, His Banker, and Venice, page 80
   A natural astringent and antiseptic, potassium alum was coveted for its medicinal and cosmetic properties. 2011, Thomas Penn, Winter King, Penguin, published 2012, page 201
2. (chemistry) Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations.
   With weld and cochineal, which are colouring matters the most sensible to the action of sulphate of iron, the purified alums gave us colours more brilliant, fresh, and in a slight degree lighter; while those with our common alums were all duller, and evidently of a deeper hue. 1807, William Nicholson, editor, A Journal of Natural Philosophy, Chemistry, and the Arts, volume XVIII, page 286
   For similar reasons, aluminium sulphate and alums are used in dyeing cloth.[…]Normally alums are soluble in water and insoluble in alcohols. 2000 June, Competition Science Vision, page 486
   In structure, the alums consist of simple ions, being not complexes, but double salts. Potash alum or potassium alum is the common alum, with the formula KAl(SO₄)₂·12H₂O) which, for convenience, may be written K₂SO₄·Al₂(SO₄)₃·24H₂O 2005, Amit Arora, Text Book Of Inorganic Chemistry, page 386

verb

1. (transitive) To steep in, or otherwise impregnate with, a solution of alum; to treat with alum.
   The silk should be boiled at the rate of 20 parts of soap per cent. , and then alumed. The aluming need not be so strong as for the fine crimson 1839, Andrew Ure, A Dictionary of Arts, Manufactures, and Mines

Etymology 2

From alumnus and alumna (> alumn- > alum), by the removal of the originally Latin gender-specific nominative singular case endings -us (masculine) and -a (feminine).

noun

1. (shortening, Canada, US) A past attendee or graduate (of either gender) of a college, university or other educational institution.
   1961 Spring, Anchora of Delta Gamma, Volume LXXVII, No. 3, page 59, Evanston-North Shore alums are happy to open their homes to Sigma actives for special social events.
   You'll remember that we're starting with a list of slightly over 7,000 names that are alums (most of them over 50) that we'd like to whittle down to a manageable list of prospects. 2006, Ted Hart, James M. Greenfield, Pamela M. Gignac, Christopher Carnie, Major Donors: Finding Big Gifts in Your Database and Online, page 47
   All schools that last have alums, and, ancient as it was by American standards, Trinity by mid-century had thousands. 2009, Timothy C. Jacobson, Charity & Merit: Trinity School at 300, page 190