MEANINGS

The noun avoirdupois denotes a system of weights based on a pound of 16 ounces or 7,000 grains, widely used in English-speaking countries.

The word is also used humorously in the sense of a person’s heaviness, weight.

ORIGIN

The noun avoirdupois is an altered spelling of avoir de pois, from early Old French and Anglo-Norman aveir de peis, meaning goods of weight; the Norman form peis was from around 1300 varied with, and around 1500 superseded by, the Parisian form pois.

The Old-French noun aveir de peis, avoir de pois, is composed of:
– the noun use (meaning property, goods, aver) of the infinitive aveir, avoir (meaning to have – from the Latin verb hăbēre, of same meaning);
– the preposition de, meaning of;
– the noun peis, pois, from an assumed Late-Latin form pesum, alteration of classical Latin pensum, weight—see linguistic notes.

Around 1640-50, “some ignorant ‘improver’” (as the Oxford English Dictionary put it in its first edition of 1885) introduced du instead of de, and the word became avoirdupois.

The French word du, contraction of the preposition de and of the definite article le, translates:
– either as of the, as in homme du monde, man of the world,
– or as the indefinite determiner some, as in je voudrais du sucre, I’d like some sugar.

Now, goods of the weight makes little sense and goods some weight none, so that avoirdupois can only translate as to have (some) weight; this has resulted in a misinterpretation of the word in Νομο-λεξικον [= Nomo-Lexikon]: A Law Dictionary (2^nd edition – London, 1691), by the English lexicographer Thomas Blount (1618-79), who wrote that avoirdupois is from French avoir du poids, which he translated as Latin habere pondus, to have (some) weight; he mistakenly added that “it is (probably) so called, because it is of more weight than the other [= Troy-weight]”.

This has resulted in two standard pronunciations of avoirdupois: one, /ˌavədəˈpɔɪz/ in the International Phonetic Alphabet (IPA), shows the original form of the word; the other, /ˌavwɑːdjʊˈpwɑː/, shows its later form.

The original meaning of avoirdupois, therefore, was goods sold by weight, as distinguished from the goods sold by measure or number; for instance, the following act was passed in 1353, during the reign (1327-77) of King Edward III (1312-77):

Some Merchants buy Avoir-de-pois, Wools, and other Merchandize by one Weight, and sell by another, and make also deceitful Draughts upon the Weight, and also use false Measures and Yards, in great Deceit of us, and of all the Commons, and of lawful Merchants; therefore it is established, that one Weight, one Measure, and one Yard, be through all the Land: And that Wools, and all Manner of Avoir-de-pois, be weighed by Balances.
(source: Reports from Committees of the House of Commons – 1737)

From the sense of goods sold by weight, the word avoirdupois (more fully avoirdupois weight) came to be used as the name of the standard system of weights used in Great Britain for all goods—with the exception of the precious metals, precious stones, and medicines, for which the troy weight system is used.

In the above-mentioned law dictionary, Thomas Blount still distinguished between the derived sense, system of weights, and the primary sense, goods sold by weight:

Avoir du Pois […] Signifies, First, a kind of weight different from that which is called Troy-weight, containing but Twelve ounces to the pound, whereas this hath Sixteen. And in this respect it is (probably) so called, because it is of more weight than the other. 2. It signifies such Merchandises as are weighed by this weight, and not by Troy-weight.

Linguistic notes:
Latin pensum is from the verb pendĕre, to weigh, literally to cause to hang down, to suspend; it was specially used of scales in weighing. The -d- in Modern French poids, weight, is due to mistaken association with Latin pondus, weight, from the verb pendĕre. In French, peser means to weigh, and pendre means to hang. The English noun pound is from Latin pondō, short for lībra pondō, literally a pound (= lībra) by weight (= pondō)—Latin lībra denoted the Roman pound of twelve ounces, and pondō was a form of pondus, meaning weight—cf. linguistic pondering over ‘Libra’ and ‘pound’.

From Old French, English also had the collective singular noun aver, meaning possession, property, estate, wealth, money. As a count noun, aver denoted a beast of burden, a draught ox or horse; it was specially used in the sense of a horse used for heavy work, a cart-horse, and in later usage, in northern dialects, an old or worthless horse. In the above-mentioned law dictionary, Thomas Blount translated the Latinised plural form affri, or affra, as “Bullocks, or Plough-horses”; he added that “in Northumberland, to this day, they call a dull or slow Horse, a False aver, or Afer”.

Note about the troy weight system:
The noun troy, or troy weight, designates a system of weights used mainly for precious metals and gems, with a pound of 12 ounces or 5,760 grains; it seems to have taken its name from a weight used at the fair of Troyes, a town in northern France, on the River Seine, capital of the former province of Champagne.