pilot light

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A small jet of gas that is kept burning in order to ignite a gas burner, as in a stove. Also called pilot burner.
2. n. See pilot lamp.

Century Dictionary and Cyclopedia

1. n. A very small gaslight kept burning beside a large burner, so that when the flow through the main burner is turned on it will be automatically lighted by the pilot-light. It is usually protected by a shield from being accidentally blown out. See by-pass.
2. n. A lamp placed on a dynamo to show that it is working properly.
3. n. A small burner burning continuously, used in motor-car practice to ignite the main burner when the demand for power exceeds the supply of energy stored in the generator from a previous ignition.

Wiktionary

1. n. A small, persistent flame used to ignite gas.

GNU Webster's 1913

1. n. a small gas flame kept burning continuously on a stove, water heater, or other gas-burning device, so as to allow immediate ignition of the main flame when the gas flow is turned on.

WordNet 3.0

1. n. indicator consisting of a light to indicate whether power is on or a motor is in operation
2. n. small auxiliary gas burner that provides a flame to ignite a larger gas burner