gravity knife

Etymology
. From being a folding knife that could be opened by allowing gravity to draw out the blade.

Noun

 * 1) A type of knife that with the press of a button, allows the blade to drop out of the handle, and then quickly opened up full, for quick use, also allowing it to be flicked open with a flick of the wrist.
 * 2) A folding knife of this type.
 * 3) A telescoping knife of this type.

Coordinate terms

 * a type that overlaps with gravity types
 * spring-loaded opening knife
 * spring-loaded opening knife