The word
ounce ultimately comes from the Latin word
uncia, meaning "one-twelfth." (This is also where we get the word
inch.) In Italian, this became
onzo, which is where we get both the word
ounce and its abbreviation,
oz.
"But," you say, "there are 16 ounces in a pound, not 12!" It's true that in the international
avoirdupois system, 1 pound equals 16 ounces, but this wasn't always the case. In ancient Rome, a pound (
libra in Latin, which is where the abbreviation
lb. comes from) was about 12 ounces. Even today, jewels and precious metals are measured in
troy ounces (which are heavier than avoirdupois ounces), and there are 12 troy ounces in a
troy pound(which is lighter than an avoirdupois pound).