plural serums or sera /ˈsirə/ plural serums or sera /ˈsirə/ Learner's definition of SERUM
1
[noncount] medical : the part of blood that is like water and that contains substances (called antibodies) that fight disease血清；抗毒血清 2
medical : serum from an animal's blood that can be added to a person's blood to prevent or cure disease免疫血清 [noncount]
[count]
3
[noncount] biology : the watery part of a fluid found in a plant（植物的）浆液，树液