serum

noun (plural sera /-rə/ or serums)

• 1an amber-coloured, protein-rich liquid which separates out when blood coagulates: the researchers examined blood serum obtained from 471 heterosexual men and women [count noun]:sera were stored at −20°C until tested

• 2the blood serum of an animal used to provide immunity to a pathogen or toxin by inoculation or as a diagnostic agent: doctors treated the bites of carpet vipers with serum produced from local snakes