'lymphocyte-activating' originates from the combination of 'lymphocyte' (from Greek 'lymphē' meaning 'clear fluid' and 'kytos' meaning 'cell') and 'activate' (from Latin 'activare' via Old French 'activer'), where 'lymph-' meant 'clear fluid' and 'kytos' meant 'cell'.

'lymphocyte' developed via New Latin/medical Latin from Greek elements ('lymphē' + 'kytos') and entered English as 'lymphocyte'; 'activate' comes from Latin 'activare' -> Old French 'activer' -> Middle/Modern English 'activate'; the compound 'lymphocyte-activating' is a modern scientific formation used in biomedical English.

Initially, 'activate' meant 'make active'; combined as 'lymphocyte-activating' it has been used in scientific contexts to mean 'causing activation of lymphocytes', a specialized technical meaning that has remained consistent.