A metric unit of distance equal to 1000 kilometers or about 621.371 miles. Although this appears to be an appropriate unit for longer distances on the earth, the megameter is seldom used
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}