Noun

1. Any of several mechanisms that regulate the periodicity of biological functions
2. The progression from puberty to menopause during which a woman can bear children

Quotations

• 2005 US Department of Health - Your guide to healthy sleep

  Your biological clock is actually a tiny bundle of cells in your brain that responds to light signals received through your eyes.

• 1994 Rugh Winter, Bonnie Eaker-Weil - Adultery, the Forgivable Sin

  Take Linda, a thirty-nine-year-old newscaster who relished her career but began to hear the alarm ringing on her biological clock.