time
n. a concept by which events are ordered into past, present, and future. Through the observation of recurrent phenomena, such as the rotation of the earth, time is divided into periods and used to measure the duration of events and rates of change. Time appears to be so abstract, and at the same time so fundamental, that no universally satisfactory definition has been formulated. It is a matter of debate whether time is a construct arising from humanity’s marking of change or some sort of medium through which change occurs. Although classical mechanics regarded time as absolute, the special theory of relativity maintains that time is relative to motion. Philosophers have also differed over whether time is absolute or relative to particular perspectives and conditions.