Today’s factoid:
The earliest surviving written examples of the word “girl”, dating from 1290, used it to mean a child of either sex. A male child was called a “Knave girl” whereas a female child was termed a “gay girl”. Over time “girl” gradually came to be used exclusively for female children. There are examples dating from 1530 in which the word “girl” is used to mean “maiden” (also originally applied to both sexes), or any unmarried human female.
Source: Wikipedia.