Any of a group of steroids that are secreted by the ovaries and function as female sex hormones.
"Estrogen levels fluctuate throughout the menstrual cycle, acting as essential female sex hormones produced by the ovaries."
In plain English: Estrogen is a hormone that helps girls develop female physical traits during puberty and regulates their menstrual cycle.
"Doctors tested her blood to check if she had enough estrogen for menopause symptoms."
Usage: Estrogen is often confused with progesterone, but the two serve distinct roles in the menstrual cycle and pregnancy. Use this term specifically when referring to the hormone itself rather than general feminine characteristics or behaviors.
The word estrogen combines the root estro- from estrus with -gen, meaning a producer. It entered English to describe the hormone that triggers heat in female animals and influences human reproductive development.