'antineoplastic' originates from Greek elements via New Latin/Modern medical usage: the prefix 'anti-' from Greek 'anti-' meaning 'against' combined with 'neoplastic' (from 'neo-' + 'plastic').

'antineoplastic' was formed in modern medical English by adding the prefix 'anti-' to 'neoplastic' (itself derived from New Latin 'neoplasma'/'neoplasm', from Greek 'neos' 'new' + 'plasma' 'that which is formed'), and entered clinical usage in the 20th century to describe agents opposing tumor growth.

Literally it meant 'against new formation', but over time it came to mean specifically 'opposing the formation or growth of neoplasms (tumors)', i.e., drugs or treatments used in cancer therapy.