1. A stone marker set up on a roadside to indicate the distance in miles from a given point.
2. An important event, as in a person's career, the history of a nation, or the advancement of knowledge in a field; a turning point.

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.