se·rum 
/ˈsirəm/ noun
plural se·rums or se·ra /ˈsirəm/ noun /ˈsirə/ 1 [noncount] medical : the part of blood that is like water and that contains substances (called antibodies) that fight disease
▪ blood serum 2 medical : serum from an animal's blood that can be added to a person's blood to prevent or cure disease [noncount] ▪ The patient was administered serum. [count] ▪ mouse sera 3 [noncount] biology : the watery part of a fluid found in a plant
▪ blood serum
