'autocombustible' is formed from the prefix 'auto-' (from Greek 'autos' meaning 'self') + 'combustible' (from French/Latin 'combustibilis', related to Latin 'comburere'/'combust-').

'combustible' comes from Latin 'combustibilis' (from past participle 'combustus' of 'comburere'/'urere' meaning 'to burn'), moved into Old French as 'combustible' and then into English. The modern formation 'autocombustible' is a compounding using the Greek-derived prefix 'auto-' joined to the existing English adjective 'combustible'.

Initially the elements meant 'self' (auto-) and 'able to be burned' (combustible); over time the compound came to be used to describe materials or substances that can ignite by themselves — 'capable of self-ignition'.