The term 'stealthy assassin' is often used to describe a NINJA, which is a type of Japanese martial artist. Ninjas were known for their ability to move silently and quickly, as well as their use of weapons and tactics to surprise their opponents. They were also known for their ability to blend into the shadows and remain undetected. The term 'stealthy assassin' is an apt description of a NINJA, as they were trained to be both silent and deadly.