1660s (trans.), "kindle or set on fire, cause to burn," from Latin ignitus, past participle of ignire "set on fire, make red hot," from ignis "fire" (see igneous). Attested earlier as an adjective (1550s). Intransitive sense of "catch fire, begin to burn" is from 1818. Related: Ignited; igniting.
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.
in geology, "large, intrusive body of igneous rock formed beneath the earth's surface," 1936, Modern Latin, from the geological sense of plutonic (q.v.).
