toboggan

Short definition from Wiktionary

Noun

1. 1
   A long sled without runners, with the front end curled upwards, which may be pulled across snow by a cord or used to coast down hills.
2. 2
   A similar sled of wood, pulled by dogs, possibly with steel runners, made to transport cargo.
3. 3
   Something which, once it starts going (figuratively) downhill, is unstoppable until it reaches the bottom.
4. 4
   A knit cap, designed to provide warmth in cold weather.

Verb

1. 1
   To slide down a hill on a toboggan or other object.
2. 2
   To go downhill unstoppably until one reaches the bottom.
3. 3
   To fly sharply downward so as to build up speed to facilitate in-flight refueling of a faster aircraft.