Source : Webster's Revised Unabridged Dictionary (1913)

Slow \Slow\, v. t. [imp. & p. p. {Slowed}; p. pr. & vb. n.
   {Slowing}.]
   To render slow; to slacken the speed of; to retard; to delay;
   as, to slow a steamer. --Shak.

Source : WordNet®

slowing
     n : a decrease in speed; "the deceleration of the arms race"
         [syn: {deceleration}, {retardation}] [ant: {acceleration}]