"action or process of burning," early 15c., from Old French combustion (13c.) and directly from Latin combustionem (nominative combustio) "a burning," noun of action from past-participle stem of Latin comburere "to burn up, consume," from com-, here perhaps an intensive prefix (see com-), + *burere, based on a faulty separation of amburere "to burn around," which is properly ambi-urere, from urere "to burn, singe" (from PIE root *heus- "to burn;" see ember).
"capable of burning," 1520s, from French combustible, or directly from Late Latin combustibilis, from Latin combustus, past participle of combuere "to burn up, consume" (see combustion). Figurative sense "easily excited" is from 1640s. As a noun, "a substance that will burn," from 1680s. Related: Combustibility (late 15c.).
"to inflame, to burn," late 15c., from Latin combustus, past participle of combuere "to burn up, consume" (see combustion). "Now only jocular or affected" [OED]. Related: Combusted; combusting. Combust was used in Middle English from late 14c. as a past-participle adjective, "burnt," from Old French combust (14c.) and directly from Latin combustus. Also it was an astrological term for planets when near the sun.
1610s, "act of heating to the point of combustion," from French ignition or directly from Medieval Latin ignitionem (nominative ignitio), noun of action from past-participle stem of Latin ignire "set on fire," from ignis "fire" (see igneous). Meaning "means of sparking a fire" (originally in a gun) is from 1881; meaning "means of sparking an internal combustion engine" is from 1906.
"waste gas," 1848, originally from steam engines, from exhaust (v.). In reference to internal combustion engines by 1896. Exhaust pipe, which carries away waste gas or steam from an engine, is by 1849.
indicating the sound of a muffled internal combustion engine, 1904, imitative. Applied to various engines or objects which make such a sound.