Definition of 「両」:
1. Anciently the same as "two".
古同“两”。
2. Ideogram.
会意。
3. Chinese unit of weight in the market system. The system originates from the weight of the yellow bell. One yi (a traditional measure) holds twelve hundred grains of millet, weighing twelve zhu (a traditional weight unit); thus, two (两) refers to the weight equivalent to twenty-four zhu, and sixteen (两) makes a jin (斤). Therefore, both refer to the weight of two yellow bell weights. — From "Book of Han, Records of Law and Calendar"
中国市制重量单位。衡权…本起于黄钟之重。一龠容千二百黍,重十二铢,两之为两,二十四铢为两,十六两为斤。…两者,两黄钟律之重也。——《汉书·律历志上》