n. The act of igniting, kindling, or setting on fire.n. Means of igniting; provision for firing.n. The state of being ignited; a burning.n. In chem., the process of roasting or intensely heating a substance.n. In internal-combustion motors, the setting fire to the mixture of air and hydrocarbon vapor in the cylinder, so that the air shall expand and increase its pressure and perform the work required.