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earth (ûrth)
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n.
1.
a. The land surface of the world.
b. The softer, friable part of land; soil, especially productive soil.
2. oftenEarthThe third planet from the sun, having a sidereal period of revolution about the sun of 365.26 days at a mean distance of approximately 149.6 million kilometers (92.96 million miles), a sidereal rotation period of 23 hours 56.07 minutes, an average radius of 6,378.1 kilometers (3,963 miles), and a mass of approximately 5.9736 × 1024 kilograms (1.3169 × 1025 pounds).
3. The realm of mortal existence; the temporal world.
4. The human inhabitants of the world:The earth received the news with joy.
5.
a. Worldly affairs and pursuits.
b. Everyday life; reality:was brought back to earth from his daydreams of wealth and fame.
6. The substance of the human body; clay.
7. The lair of a burrowing animal.
8. Chiefly British The ground of an electrical circuit.
9. Chemistry Any of several metallic oxides, such as alumina or zirconia, that are difficult to reduce and were formerly regarded as elements.
v.earthed, earth·ing, earths
v.tr.
1. To cover or heap (plants) with soil for protection.
2. To chase (an animal) into an underground hiding place.
v.intr.
To burrow or hide in the ground. Used of a hunted animal.
Idiom:
on earth
Among all the possibilities:Why on earth did you put on that outfit?

[Middle Englisherthe, fromOld Englisheorthe; see er-2 in the Appendix of Indo-European roots.]
(click for a larger image)
earth
cutaway of the earth

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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