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Nep·tune (nĕptn, -tyn)
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n.
1.
a. Roman Mythology The god of water, later identified with the Greek Poseidon.
b. The sea.
2. The eighth planet from the sun, having a sidereal period of revolution around the sun of 164.8 years at a mean distance of 4.5 billion kilometers (2.8 billion miles), a mean equatorial diameter of 49,528 kilometers (30,775 miles), and a mass 17.25 times that of Earth.

[Latin Neptūnus.]

Nep·tuni·an (-tnē-ən, -ty-) adj.
(click for a larger image)
Neptune
top:the Roman god
bottom: the planet Neptune
(click for a larger image)
Neptune

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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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