jumping jack

plural jumping jacks · alternative jumping-jack

1. A physical exercise performed by jumping to a position with the legs spread wide and the hands touching overhead and then returning to a position with the feet together and the arms at the sides.

   Synonyms: side-straddle hop, star jump

2. A machine, roughly the size of a three-year-old child, the foot of which vibrates forcefully, causing it to "jump" rapidly, pounding the ground to compact it.
3. datedA toy figure of a person with jointed limbs that can be made to appear to dance or jump by pulling an attached string.

   Synonyms: quockerwodger