Component in a combustion engine (9)
(Other definitions for spark plug that I've seen before include "Electrical device fitted in the cylinder heads of an internal-combustion engine" , "Agent of ignition" , "Ignition device in an internal-combustion engine" , "engine component" , "Does it help to start driving" .)
(Other definitions for sparkplug that I've seen before include "that'll help get jaguar running" , "Agent of ignition" .)