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Huy·gens' principle

(hīgənz)

The principle that any point on a wave front may be regarded as a central source of secondary waves; the sum of these waves determines the propagation of the wave.

[After Christiaan Huygens.]

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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