1520s, from Middle French combustible, or directly from Late Latin combustibilis, from Latin combustus, past participle of combuere "to burn up, consume" (see combustion). Figurative sense is from 1640s; as a noun, from 1680s. Related: Combustibility (late 15c.).
combustible com·bus·ti·ble (kəm-bŭs'tə-bəl)
Capable of igniting and burning. n.
A substance that ignites and burns readily.