Answer: biorhythm

AnswerCrossword Clue
biorhythma periodic change in the behaviour or physiology of many animals and plants (eg hibernation and migration) mediated by hormones which are in turn influenced by changes in day-length
biorhythmA recurring cycle in the physiology or functioning of an organism, such as the daily cycle of sleeping and waking
biorhythmA cyclic pattern of physical, emotional, or mental activity said to occur in the life of a person