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rule of thumb

n. pl. rules of thumb

A useful principle having wide application but not intended to be strictly accurate or reliable in every situation.

[From the use of the thumb as a makeshift ruler or measuring device, as in carpentry.]

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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