A unit of force based upon the pound, foot, and second, being the force which, acting on a pound avoirdupois for one second, causes it to acquire by the of that time a velocity of one foot per second. It is about equal to the weight of half an ounce, and is 13,825 dynes.

a unit of force equal to the force that imparts an acceleration of 1 foot/sec/sec to a mass of 1 pound; equal to 0.1382 newtons

The poundal is a non-SI unit of force. It is a part of the absolute foot-pound-second system of units, a coherent subsystem of English units introduced in 1879, and one of several specialized subsystems of mechanical units used as aids in calculations. It is defined as 1 lb·ft·s-2, or in words, as the force necessary to accelerate a pound of mass at 1 foot per second, per second. 1 pdl = 0.138 254 954 376 newton (N) exactly.