Bujinkan is a traditional martial art form that originated in Japan and is popularly known for its effective techniques and defensive tactics. As the term is specific to this form of martial art, there may not be many synonyms for it. However, some alternative expressions could be "Ninjutsu" or "Ninpo," which are other traditional Japanese martial arts that share similarities with Bujinkan. Another word that could be used is "Togakure Ryu," which is a specific school within the Bujinkan. Overall, the word Bujinkan is specific to this martial art and has not many equivalent words in English.