A third rail is a live rail beside the track that powers the train. Step over the third rail.
It is uninsulated and lethal, which is why trespass on those lines is so dangerous. A third rail is also a phrase for a subject in politics nobody dares touch.
1nounthird railA live rail beside the track that powers the train.
“The third rail runs the whole southern network.”
third rail is a rail.
Practised in Railways