headspring

Short definition from Wiktionary

Noun

1. 1
   A fountainhead; a source.
2. 2
   A basis or foundation.
3. 3
   A move in which the gymnast places both hands on the mat with the top of the head about 6 inches in front, pushes off with the hands while flipping the legs overhead, and lands on the feet.
4. 4
   A spring that sits at the top of a mechanism, pushing the internal parts inward.

Verb

1. 1
   To perform a headspring.