serum

 
Pronunciation: /ˈsɪərəm/

noun (plural sera /-rə/ or serums)

[mass noun]
  • 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

Origin:

late 17th century: from Latin, literally 'whey'