Chronobiology is a field that studies the effects of time on biological systems. Periodicity is of particular interest. The master biological clock in the suprachiasmatic nucleus controls daily rhythms of core body temperature, rest-activity cycle, physiological and behavioral functions, psychomotor functions and mood in humans. Time is a concept. Can we use the word “chronobiology” instead of “biorhythm”? Biological clock, arrow of time and chronobiology, belong to a terminology as imprecise as phantasmatic; they are unsuitable.