ninjutsuPronunciation: /nɪnˈdʒʌtsuː/Definition of ninjutsu noun [mass noun] the traditional Japanese art of stealth, camouflage, and sabotage, developed in feudal times for espionage and now practised as a martial art. Origin:Japanese, from nin 'stealth' + jutsu 'art, science'ninjutsu in other Oxford dictionaries Definition of ninjutsu in the US English dictionary