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Synonyms

fault line

American  

noun

Geology.

  1. the intersection of a fault with the surface of the earth or other plane of reference.

fault line British  

noun

  1. Also called: fault plane.  geology the surface of a fault fracture along which the rocks have been displaced

  2. a potentially disruptive division or area of contention

    Europe remains the main fault line in the Tory Party
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of fault line

First recorded in 1865–70

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

He astutely flags “medical gatekeeping” as an emerging fault line.

From The Wall Street Journal • Feb. 8, 2026

“The deeper fault line here is not trade flows. It is capital,” wrote Stephen Innes, managing partner at SPI Asset Management, in a Sunday note.

From MarketWatch • Jan. 19, 2026

"This is significant because it means the ground shaking near the fault line might be more intense than our current hazard models predict for these types of faults."

From Science Daily • Dec. 16, 2025

He cited safety concerns—the plant sits on a fault line.

From Barron's • Nov. 18, 2025

Seeing her so changed made me feel as if I stood on a fault line and any moment my whole life might crack apart.

From "Hope Springs" by Jaime Berry

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.