Mars

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Roman Mythology The god of war.
• noun The fourth planet from the sun, having a sidereal period of revolution about the sun of 687 days at a mean distance of 227.9 million kilometers (141.6 million miles) and a mean diameter of approximately 6,794 kilometers (4,222 miles).

from The Century Dictionary.

• noun A Latin deity, identified at an early period by the Romans with the Greek Ares, with whom he had originally no connection.
• noun The planet next outside the earth in the solar system.
• noun In old chemistry, iron.
• noun In heraldry, the tincture red, when blazoning is done by the planets: see blazon.

from the GNU version of the Collaborative International Dictionary of English.

• proper noun (Rom. Myth.) The god of war and husbandry.
• proper noun (Astron.) One of the planets of the solar system, the fourth in order from the sun, or the next beyond the earth, having a diameter of about 4,200 miles, a period of 687 days, and a mean distance of 141,000,000 miles. It is conspicuous for the redness of its light.
• proper noun (Alchemy), Archaic The metallic element iron, the symbol of which ♂ was the same as that of the planet Mars.
• proper noun a bright, somewhat yellowish, brown.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun The Mars Bar, a brand of chocolate bar with caramel and nougat filling.
• proper noun Roman mythology The Roman god of war.
• proper noun astronomy The fourth planet in the solar system. Symbol: ♂

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Roman mythology) Roman god of war and agriculture; father of Romulus and Remus; counterpart of Greek Ares
• noun a small reddish planet that is the 4th from the sun and is periodically visible to the naked eye; minerals rich in iron cover its surface and are responsible for its characteristic color