"covered truck or wagon," 1829, shortening of caravan. Century Dictionary suggests this was perhaps regarded as *carry-van.
1776, "to stab," from jack-knife (n.). Intransitive meaning "to fold or bend" the body is said to date from the time of the American Civil War. The truck accident verbal sense is from 1949. Related: Jackknifed; jackknifing.
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).