Which term denotes a lack of movement?

The term that denotes a lack of movement is 'motionless.' This term directly describes a state of not moving at all, which conveys the idea of complete stillness. When something is motionless, it is entirely devoid of any movement, making it the most accurate choice for describing a lack of movement.

In contrast, while 'static' can imply a lack of movement, it often suggests stability or being unchanging rather than the absence of motion itself. 'Lethargy' refers to a state of sluggishness or inactivity, commonly associated with a lack of energy, rather than the absence of physical movement. 'Motion,' on the other hand, explicitly indicates movement, which is the opposite of a lack of movement. Thus, 'motionless' is the most fitting term to describe a complete lack of movement.