'antisera' originates from Neo-Latin, specifically from the formation 'antiserum', where the prefix 'anti-' comes from Greek 'anti' meaning 'against' and 'serum' comes from Latin 'serum' meaning 'whey' or 'watery fluid'.

'serum' entered English from Latin 'serum' (originally 'whey'); in the late 19th century the scientific Neo-Latin coinage 'antiserum' (anti- + serum) was created to denote serum used against toxins or microbes. The English plural follows the Neo-Latin/Latin pattern, forming 'antisera' from 'antiserum'.

Initially it specifically meant 'serum used against a particular disease or toxin' (especially antitoxin sera); over time the term's core meaning has remained but broadened to include sera used both therapeutically (passive immunization) and diagnostically.