The Collaborative International Dictionary of English v.0.48:

Jujutsu \Ju"jut`su\, Jujitsu \Ju"jit`su\, Jiujutsu \Jiu"jut`su\,
Jiujitsu \Jiu"jit`su\ n. [Jap. j[=u]jutsu; j[=u] soft (prob.
   because no weapons are used) + jutsu art.]
   The Japanese art of self-defense without weapons, now widely
   used as a system of physical training. It depends for its
   efficiency largely upon the principle of making clever use of
   an opponent's strength, weight, and movements to disable or
   injure him, and by applying pressure so that his opposing
   movement will throw him out of balance, dislocate or break a
   joint, etc. It opposes knowledge and skill to brute strength,
   and demands an extensive practical knowledge of human
   anatomy.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

jujutsu
    n 1: a method of self-defense without weapons that was developed
         in China and Japan; holds and blows are supplemented by
         clever use of the attacker's own weight and strength [syn:
         jujutsu, jujitsu, jiujitsu]