'antiserum' originates from the prefix 'anti-' (from Greek ἀντί meaning 'against') combined with 'serum' (from Latin 'serum' meaning 'whey' or 'clear liquid of milk/blood').

'antiserum' was formed in modern medical usage (late 19th to early 20th century) by combining 'anti-' + 'serum' to name sera used against specific toxins or pathogens; it entered English in medical literature and became the standard term.

Initially it referred specifically to sera used to neutralize toxins (e.g., antitoxins); over time it has been used more broadly for sera containing antibodies used for passive immunization or therapy.