Noun; the strength and vitality required for sustained physical or mental activity; a feeling of possessing such strength and vitality; force or vigor of expression; a person's physical and mental powers, typically as applied to a particular task or activity; power derived from the utilization of physical or chemical resources, esp. to provide light and heat or to work machines; the property of matter and radiation that is manifest as a capacity to perform work; a degree or level of this capacity possessed by something or required by a process.