from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A line connecting the waterfalls of nearly parallel rivers that marks a drop in land level.
- n. The natural line of descent, as for skiing, between two points on a slope.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A geomorphologic unconformity marking a boundary between an upland region and a plane; sometimes marked by a series of waterfalls on rivers that cross it.
- n. The imaginary line downhill that something falling downhill would naturally follow.
Sorry, no etymologies found.
I arrived at the top of the lowest-angle fall line that started at thirty-eight degrees and eased off to about thirty-two degrees above a cluster of twenty fully grown pine trees.