Plain English Meaning

A big electrical switch that lets the small starter switch in the cockpit safely turn on the very high current needed to spin the starter motor.

Full Definition

A heavy-duty, electrically operated switch (a high-current relay) that connects the aircraft battery to the starter motor when the pilot engages the start function. A small control current from the starter switch energizes the contactor's coil, which then closes a much larger set of contacts capable of carrying the high current the starter motor draws.

Context Anchor

Seen in aircraft starting system descriptions and during troubleshooting when the engine starter does not operate normally.