word-forming element meaning "of fire; of fire and; of igneous origin," from Latin igneus (see igneous).

"will o' the wisp, jack-o-lantern," 1560s, Medieval Latin, literally "foolish fire;" see igneous + fatuous. "It seems to have been formerly a common phenomenon; but is now exceedingly rare" [OED].

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.

"vomiting fire," c. 1600, from Late Latin ignivomous, from Latin ignis "fire" (see igneous) + vomere "to vomit" (see vomit (n.)).