ninja has definitions from the fields of sociology,work
1
[ noun ] (work) a member of the ninja who were trained in martial arts and hired for espionage or sabotage or assassinations; a person skilled in ninjutsu

Related terms

mercenary

2
[ noun ] (sociology) a class of 14th century Japanese who were trained in martial arts and were hired for espionage and assassinations

Related terms

class Japanese

*