As a boy's name, Kit arrived as a nickname for Christopher, before Chris was so popular. Christopher Columbus named the island of St. Kitts after himself, and a little for Saint Christopher. The frontiersman Kit Carson is another example, while Kit Marlowe was an Elizabethan playwright, and Kit Harington plays Jon Snow on "Game of Thrones." As a girl's name, it has been used as a nickname for Katherine. In 1944 Bette Davis played a Kit in the movie "Old Acquaintance," and the name got a slight surge in popularity. It is also the name of an American Girl doll, and it has been used in a few books as well. Americans are also used to hearing 'kit' in reference to a baby animal - namely the fox, although it has a few other meanings in the English language.
Kit has recently been more popular for boys than it has for girls, but not by much - in 2012 there were 14 girls born named Kit and 16 boys. In 2015 there were 40 boys and 28 girls. The boys also had an advantage in the early years - while it was used on boys between 1880 and 1924, it wasn't used on girls. The height of its popularity for both genders was between 1940 and 1960, but it continued being more popular for boys after 1962. Some years it is not used as a first name at all, and it has always been quite rare.