Lucky number 13’s forgotten word is: Mileway [noun] a measure of the time that it takes to walk a mile. Typically understood to be twenty minutes.
We Americans are known for describing distances in time (I’m five minutes away, etc; in our defense, a country mile, a city mile, and a Route 9 mile all mean different increments of time.), so it might surprise you to see this having parentage (Middle-English) across the pond.
Kacirk, Jeffrey. The Word Museum: The Most Remarkable English Ever Forgotten. New York: Simon & Schuster, 2000. 122. Print.