The Latin word libra describes a Roman unit of weight similar to a pound, and the abbreviation “lb” for the unit of weight and the signs £ and ₤ (crossed-out Ls) for the currency derived from this. The word “pound”

The Latin word for pound is LIBRA, and that word was once used in English when referring to money. Apparently our word "pound" comes from the Latin word "pondo" which means weight; the Latin expression seems to have been "libra pondo" for "a pound in wei

comes from the Latin pendere, “to weigh”; Latin libra means “scales, balances”.So LB is an abbreviation that has been taken to mean "pound", a measure of weight