1660s, "pertaining to or resembling fire," from Latin igneus "of fire, fiery; on fire; burning hot," figuratively "ardent, vehement," from ignis "fire, a fire," extended to "brightness, splendor, glow;" figuratively "rage, fury, passion," from PIE root *egni- "fire" (source also of Sanskrit agnih "fire, sacrificial fire," Old Church Slavonic ogni, Lithuanian ugnis "fire"). Geological meaning "produced by volcanic forces" is from 1791, originally in distinction from aqueous. Earlier in the sense "fiery" were ignean (1630s), ignic (1610s).
late 14c., "act of expelling contents of the stomach through the mouth," from Anglo-French vomit, Old French vomite, from Latin vomitus, from vomitare "to vomit often," frequentative of vomere "to puke, spew forth, discharge," from PIE root *weme- "to spit, vomit" (source also of Greek emein "to vomit," emetikos "provoking sickness;" Sanskrit vamati "he vomits;" Avestan vam- "to spit;" Lithuanian vemti "to vomit," Old Norse væma "seasickness"). In reference to the matter so ejected, it is attested from late 14c.
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Harper, D. (n.d.). Etymology of ignivomous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/ignivomous