| The American Heritage® Dictionary of the English Language: Fourth Edition. 2000. |
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| biological clock |
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| NOUN: | 1. An internal mechanism in organisms that controls the periodicity of various functions or activities, such as metabolic changes, sleep cycles, or photosynthesis. 2. The progression or time period from puberty to menopause, marking a woman's ability to bear children.
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| The American Heritage® Dictionary of the English Language, Fourth Edition. Copyright © 2000 by Houghton Mifflin Company. Published by the Houghton Mifflin Company. All rights reserved. |
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