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ax·i·om (ăksē-əm)
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n.
1. A self-evident or universally recognized truth; a maxim: “It is an economic axiom as old as the hills that goods and services can be paid for only with goods and services” (Albert Jay Nock).
2. An established rule, principle, or law.
3. A self-evident principle or one that is accepted as true without proof as the basis for argument; a postulate.
[Early Modern English, from Latin axiōma, axiōmat-, from Greek, “that which is thought to be worthy (as of assent),” axiom, from axioun, to think worthy, from axios, worthy; see ag- in the Appendix of Indo-European roots.]
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:

    Indo-European Roots

    Semitic Roots

    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.

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