missy (n.)

"the term of honour to a young girl" [Johnson], originally (17c.) a shortened form of mistress (compare Mrs., pronounced mis-ez). By 1640s as "prostitute, concubine." By 1700 as "a young, unmarried woman."

Misses as a trade term (originally in the mail order business) for sizes or styles of clothes for girls from about 10 to 17 years old is by 1880. Miss America is from 1922 as the title bestowed on the winner of an annual nationwide U.S. beauty/talent contest. Earlier it meant "young American women generally" or "the United States personified as a young woman," and it also was the name of a fast motor boat. In the 1811 reprint of the slang dictionary, Miss Laycock is given as an underworld euphemism for "the monosyllable."