Definition of "linchpin" []

• A locking pin inserted in the end of a shaft, as in an axle, to prevent a wheel from slipping off. (noun)
• A central cohesive element: Reduced spending is the linchpin of their economic program. (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.

• "Times have now changed, Schumer said, and passing a bill is possible by separating illegal from legal immigrants with what he calls the linchpin: a biometric Social Security card that includes digital records of personal characteristics."
• "More to the point, it would have to survive without McShane as Silas, continue to function dramatically even after the Saul counterpart dies and its linchpin is gone — which seems, at the moment, inconceivable."
• "Outlook: The reigning Class AA State Federation champions may run three guards but their linchpin is 6-0 Mike Coburn (16.5 ppg, 6 apg)."