pus

膿 is composed of the radical 肉 (flesh) and 農 (farm). 農 means to cultivate or farm. Plants grow densely in a field. Therefore, 膿 conveys the idea of accumulating a large quantity of meat. When a large amount of meat is stockpiled, it easily rots. The original meaning of 膿 is to rot or decay, and nowadays it refers to pus.