Why Is 'Pound' Abbreviated 'lb'?

Date: 03/08/2004 at 19:19:13
From: Lauren
Subject: about pound

Why is "pound" abbreviated lb?  The abbreviation does not match the
word.  Is it because of its Latin roots?  I know libra means pound,
but what is the real answer?  What is the history of it?

Date: 03/08/2004 at 23:31:19
From: Doctor Peterson
Subject: Re: about pound

Hi, Lauren.

Apparently you know the answer: the abbreviation is not a shortening 
of the English word pound, but of the Latin word libra, which was an 
equivalent unit.  Here is one of many discussions on the web that say 
more about it than our archives do:

    http://www.unc.edu/~rowlett/units/dictP.html 

  pound (lb, lbm, or #) [1] 
  a traditional unit of mass or weight.  The Romans used a pound
  (the libra pondo, "pound of weight") divided into 12 ounces.  All
  the countries of western Europe used similar units, divided into
  12 or 16 ounces, until the advent of the metric system.  12-ounce
  pounds were common in Italy and southern France, but in Spain
  and northern Europe 16-ounce pounds became the norm.  The word
  libra is used for this unit in Italy, Spain, and Portugal; in
  France it is called the livre.  Further north, the Latin word
  pondo ("weight") is the origin of the names of the English pound, 
  Dutch pond, Danish pund, German pfund, and Russian funt.  In
  England, two different "pound" units became standard.  The unit
  now in general use in the United States is the avoirdupois pound,
  so-called from a French phrase avoir du poids, literally "goods
  of weight," indicating simply that the goods were being sold by
  weight rather than by volume or by the piece.  The avoirdupois
  pound is divided into 16 ounces.  By international agreement, one
  avoirdupois pound is equal to exactly 453.59237 grams; this is
  exactly 175/144 = 1.215 28 troy pounds.  See avoirdupois weights
  for additional information.  The traditional symbol lb stands for
  libra, the Latin word for the unit.  The avoirdupois pound is
  sometimes abbreviated lb av or lb ap to distinguish it from the
  less common troy pound.

(Note that both "pound" and "lb" come from the Latin phrase "libra 
pondo"; "pound" literally means merely "weight"!)

We use mismatched abbreviations in English more than you may realize. 
Several abbreviations we use come from Latin, though we read them 
aloud in English: "etc." for "et cetera" ("and the rest") and "i.e." 
for "id est" ("that is").  And several other abbreviations for English 
words are really abbreviations of foreign words: "oz." for old Italian
"onza" (ounce), and "no." for Italian or Latin "numero" (number).

Why do we do this?  In at least some of these cases, it was because 
Latin was the main scholarly language when the abbreviations came 
into use, so people who wrote tended to think in Latin and to write 
as if they'd rather be writing Latin!  The Latin word was thought of 
as the "real" word, and the English word just as the way to
communicate with common people.  It may be that "lb" was used as an 
international standard of sorts (though I don't believe the pound had 
the same weight from one country to another); in a similar way we use 
abbreviations for chemical elements that do not match our English
names for them (such as Na for sodium, from Latin "natrium") because 
the symbols are the same in all countries though the names are not.  
In any case, English has always been a borrowing language; mixing
foreign words into English sentences has been common from the beginning.

I haven't been able to find any detailed history of the abbreviation; 
perhaps the Oxford English Dictionary would help to confirm when and 
how "lb" was first used--whether in a Latin context or English, and 
whether it meant the English pound or not.  I'll try to look it up 
next time I get a chance.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/