scale, balance, steelyard

秤 is composed of 禾 (grain) and 平 (balance). 禾 is a pictograph of a cereal plant, while 平 is a pictograph of a weighing device. As 平 later developed multiple meanings, to avoid confusion in usage, a new character was created to replace it. Grains were the primary commodity in ancient trade and frequently needed weighing, so 秤 refers to a weighing instrument.