When you’re reading through a recipe, we’ve all gotten used to seeing teaspoon abbreviated as “tsp” and pints are “pt.”, but have you ever wondered how the word pound was abbreviated as lb? It’s an odd choice, since they don’t have any letters in common. Or what about ounce shortened to “oz.” Where did that stray “z” come from?

To find out it requires a trip through English language history. The word “pound” comes from ancient Roman when the unit of measure was libra pondo, which meant "a pound by weight." The English word "pound" draw from the pondo part of the phrase, according to the BBC. However, the abbreviation “lb” is derived from the libra part of the word. Similarly, that’s why the symbol for the British pound is £, or an L with a line through it, because it also comes from libra pondo and, according to the BBC, “the pound’s value originally equated to the price of a pound of silver.” That’s not the only form of currency to take its name from the old measurement. The former Italian currency the “lira” also derives from libra.

If all this talk of libra is setting off a light bulb in your head, that’s because it’s also the name of seventh sign of the zodiac, which is typically symbolized by scales. That’s because the sign is associated with balance, and is related to weights and measurements.

As for the word ounce, according to the Encyclopedia Brittanica, it originates from the Latin word uncia, which was the name for both a Roman unit of weight and length. According to The Week, uncia was borrowed by the Anglo-Norman French as “ounce” and then lent to their neighbors in England. The abbreviation, though, came from Medieval Italian, who had taken the Latin word uncia and turned it into onza, introducing the “z” into the word. It’s unclear exactly why the “z” shows up in English abbreviations, but it’s clear that it came from Medieval Italian and then stuck around.

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