What is "jack-in-a-box"

Jack-in-a-box \Jack-in-a-box\

1. (Bot.) A tropical tree ( Hernandia sonora), which bears a drupe that rattles when dry in the inflated calyx.

2. A child's toy, consisting of a box, out of which, when the lid is raised, a figure (usually a clown) springs; also called jack-in-the-box.

3. (Mech.) An epicyclic train of bevel gears for transmitting rotary motion to two parts in such a manner that their relative rotation may be variable; applied to driving the wheels of tricycles, road locomotives, and to cotton machinery, etc.; an equation box; a jack frame; -- called also compensating gearing.

4. A large wooden screw turning in a nut attached to the crosspiece of a rude press.