1. Nautical. The edge of a sail that faces the wind.
2. The front edge of an airplane propeller blade or wing.
3. 1. The foremost position in a trend or movement; the vanguard: "a company on the leading edge of machine-tool technology" (Christian Science Monitor).
   2. Someone or something occupying such a position: "Together they are the leading edge of a new wing of historians known as cliometricians" (Timothy Foote).

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.