1. Roman Mythology. The god of war.
2. 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).

[Middle English, from Latin Mārs.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.