vb (intr) 1. to ignite or catch fire spontaneously without any external spark or flame2. (Automotive Engineering) (of diesel oil) to ignite when under pressure without any external spark
self′-ignite′
v.i. -ig•nit•ed, -ig•nit•ing. to ignite without spark or flame. [1940–45]self′-igni′tion,n.