'lymphocyte-inert' originates from modern English as a compound of 'lymphocyte' (New Latin/Greek origin) and 'inert' (from Latin). 'lymphocyte' comes from New Latin 'lymphocytus' ultimately from Greek 'lympha'/'lymphē' meaning 'clear fluid, lymph' and Greek 'kytos' meaning 'cell'. 'inert' comes from Latin 'iners' meaning 'inactive' (via Old French/Modern English).

'lymphocyte' entered scientific English in the late 19th century from New Latin 'lymphocytus' (Greek roots 'lymphē' + 'kytos'), and 'inert' entered English from Latin 'iners' (through Old French/late Latin) in the 17th century. The compound form 'lymphocyte-inert' is a modern descriptive coinage formed by combining these established components to describe lack of lymphocyte responsiveness.

Individually, 'lymphocyte' meant 'a type of immune cell' and 'inert' meant 'inactive or unreactive'; combined in modern usage they specifically denote 'not activating or responding to lymphocytes' in immunological contexts.