ignition
n.-
1 engine system (n.) B2 Upper Intermediatethe electrical system in a vehicle that starts the engine.
the mechanism or electronic system responsible for igniting the fuel-air mixture in an internal combustion engine.
ExampleThe car wouldn't start because there was a problem with the ignition.
ExampleModern vehicles often replace the traditional ignition system with electronic push-button starts that communicate wirelessly with a key fob.
Usageusually functions as an uncountable noun when referring to the system as a whole.
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2 key switch (n.) B2 Upper Intermediatethe place in a car where you put the key to start the engine.
the physical switch or receptacle into which a key is inserted to activate a vehicle's engine.
ExampleHe left his keys in the ignition and accidentally locked the car doors.
ExampleThe driver turned the key in the ignition, but the engine only produced a faint clicking sound, suggesting a dead battery.
Usageoften used with the preposition 'in'.
- ignition switch
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3 nuclear fusion (n.) C2 Proficiency Technical Sciencethe point when a nuclear reaction creates enough energy to keep itself going.
the state in which a thermonuclear fusion reaction becomes self-sustaining, requiring no further external energy input.
ExampleScientists are working hard to achieve ignition in fusion power plants.
ExampleAchieving fusion ignition represents a major milestone in clean energy research, as it proves the plasma can maintain its own temperature through internal heating.
Usageuncountable in this specialized physical sense.
Teacher's tipThis is a highly specific term in physics; students will likely only encounter it in science news or academic papers.
From French ignition.