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  • Offspring:  children.
  • Onset:  the start of, as in “the onset of symptoms.”
  • Organ:  a collection of tissues joined in a structure to serve a common function; for example, the lung, stomach, liver, skin, brain, and kidney.
  • Overproduction:  to produce more than what is needed.
  • Ovulation: release of an egg (ovum) by the ovary; this normally occurs midway through the menstrual cycle.
  • Oxidative stress: caused by an imbalance between the production of reactive oxygen and a biological system's ability to deal with it.