LIBRA

the basic Roman unit of weight, equal to 0.722 pounds avoirdupois (0.327 kg). The abbreviation lb for pound is derived from libra. One-twelfth of the libra, the Roman uncia, is the ancestor of the English ounce. The libra also is one of the nonmetric units of weight still used today in Spain, Portugal, and several Spanish-speaking countries of the Americas. Most of the New World libras weigh about the same as the U.S. avoirdupois pound.