'immunodepressant' originates from Modern Latin/Modern English, specifically formed by the combining form 'immuno-' (from Latin 'immunis', where 'immunis' meant 'exempt') and 'depressant' (from Latin 'deprimere', where 'de-' meant 'down' and 'primere' meant 'to press').

'immunodepressant' was created in English by attaching the combining form 'immuno-' to the existing word 'depressant' (itself from Latin 'deprimere' via Old French), producing a medical term meaning an agent that 'presses down' the immune response.

Initially the roots conveyed the ideas 'exempt' (immuno-) and 'to press down' (depress-); combined in the 20th century they came to denote specifically an agent that reduces immune system activity.