switchback

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A road, trail, or railroad track that follows a zigzag course on a steep incline.
2. n. A sharp bend in a road or trail on a steep incline.
3. n. Chiefly British A roller coaster.
4. v. To proceed in sharp turns in alternating directions on a steep incline: the trail switchbacked up the mountain; the hikers switchbacked up the hill.

Century Dictionary and Cyclopedia

1. Characterized by alternate motion, or by motion back and forth; pertaining to or adapted to use on a switchback: as, a switchback method of ascent; a switchback series of inclines; a switchback railway.
2. n. A railway for ascending or descending steep acclivities, in which a practicable grade is obtained by curving the track alternately backward and forward along the side of the slope. Also called switchback railway.
3. n. By extension, an inclined railway in which the movement of a train or of a car is partly or wholly effected by gravity, as in the switchback railway at Mauch Chunk, Pennsylvania, and railways constructed for purposes of amusement at watering-places, fairs, and pleasure-resorts. In many of these the car first runs down a steep incline, and by its momentum is carried up a lesser incline, alternate ascents and descents being made till the end of the course is reached.

Wiktionary

1. n. A zigzag path, road or railway track; especially a railway track in which the train travels in a reverse direction at each switch
2. n. A hairpin bend.
3. n. A roller coaster.
4. v. To zigzag.