I was watching a Trevor Noah standup on Netflix tonight and Noah made a good observation of how "lb" became an abbreviation for "pound" in america. Seeing as to how those letters aren't in that word I'm wondering how that came to be.
"lb" is short for libra, a Roman unit of weight. It was about 330g (so less than a modern pound) and was divided in twelve ounces.
In French, a romance language, the unit is still called livre (although we don't use it much more since we do everything in metric; where I'm from, we only use it for weighting butter). It is worth half a kilo, close to the US pound (454 g).
The OED says "pound" comes from the locution libra pondo (= "a libra of weight").