jackshaft

jack +‎ shaft

jackshaft (plural jackshafts)

1. A common mechanical component used to transfer or synchronize rotational force in a machine.

   Synonym: countershaft

2. A wheelless axle used to turn the wheels of a locomotive.
   • 1950 October, “S.R. Diesel-Mechanical Shunter”, in Railway Magazine, page 692:

     Final drive is by reduction gears on the jackshaft, and through flycranks and rods to the wheels.

jackshaft (third-person singular simple present jackshafts, present participle jackshafting, simple past and past participle jackshafted)

1. To transfer or synchronize rotational force by means of a jackshaft.

   Synonym: countershaft