The Collaborative International Dictionary of English v.0.48:

Poundal \Pound"al\, n. [From 5th Pound.] (Physics & Mech.)
   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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

poundal
    n 1: 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 [syn: poundal, pdl]