fail-safe or fail·safe (fālsāf′)
1. Capable of compensating automatically and safely for a failure, as of a mechanism or power source.
2. Acting to discontinue a military attack on the occurrence of any of various predetermined conditions.
3. Guaranteed not to fail: "There is no fail-safe mechanism guaranteed either to contain or to restore presidential authority" (Arthur M. Schlesinger, Jr.)
A fail-safe mechanism.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.