Jack-in-a-box Meaning, Definition & Usage

. (a) (Bot.) A tropical tree (Hernandia sonora), which bears a drupe that rattles when dry in the inflated calyx . (b) A child's toy, consisting of a box, out of which, when the lid is raised, a figure springs . (c) (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 . (d) A large wooden screw turning in a nut attached to the crosspiece of a rude press.