'antigen' originates from early 20th-century German, specifically the word 'Antigen', formed in immunological usage as a shortening of the phrase 'antibody generator' (or a compound of 'anti-' and '-gen'), where the element 'anti-' was associated with 'antibody' (or 'against') and '-gen' derives from Greek roots meaning 'to produce'.

'antigen' was coined in German scientific literature in the early 1900s and then adopted into English medical and biological terminology; it evolved from phrases describing substances that 'generate antibodies' to the concise technical term 'antigen'.

Initially, it meant 'a substance that generates antibodies'; over time the meaning broadened to refer more generally to 'any substance or molecular structure that is recognized by antibodies or T cells' (not only those that actively induce antibody production).