Definition of "third rail" []

• The rail that supplies the high voltage to power a train on an electric railway. (noun)
• A subject that tends to be avoided because of its offensive or controversial nature: "Social Security, the 'third rail' of American politics” ( Charles Stein). (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "In his haste to stab Taylor he'd ignored what was just beyond her body — what she'd been trying to sucker him into hitting the electrified third rail of the subway, which held more amperage than an electric chair."