What distinguishes these names from unisex names is their separate male and female forms. Parents who want to give their daughter a name that pays tribute to Charles, for example, are going to choose one of its feminine forms or derivatives, such as Charlotte or even Carol, a feminine form of the masculine name Carl, which is derived from Charles. And you never see these feminine forms crossing over to masculine use. In the world of naming, there truly isn’t a boy named Sue, despite the famous song by Johnny Cash. But there are a few named Mary, including one of American cinema’s most legendary tough guys.

You Can Call Me Marion, or You Can Call Me Duke

While no one knows for sure how unisex names really got started, it was probably the growing use of feminine forms of masculine names that prompted parents to appropriate other names that were once considered each gender’s sole property. Some of these names were changed very little as they made their transfer from sex to sex. Others received new spellings that made them look more feminine. In time, some of these names became so broadly used as feminine names that they almost completely lost their original male identities, such as:

Marion. This is a French variant of Mary, usually given to boys to honor the Virgin Mary or to place the bearer under her protection. Even so, it has such a strong connotation as a woman’s name that John Wayne, about the most famous Marion who ever lived, got rid of it in a hurry at the beginning of his movie career. As it’s spelled here, it’s still considered a masculine name, although it’s rarely used for either gender anymore. Exchange the “o” for an “a” and you have the feminine form, although both spellings have been used for women. Leslie. This Scottish or Gaelic place name became a surname first and then a boys’ name before the girls took it over. The standard spelling doesn’t change when used for girls, but there are a number of variants, like Leslea, Lesley, and Lezlie. While it’s almost entirely used as a girls’ name now, there are a few male Leslies still running around.

Adrian. This name, which means “from Adria,” a northern Italian city, first gained popularity in Britain and still has a British ring to it. Spell it a little differently—Adrienne, for example—and it’s a fairly popular girls’ name. It’s probably in broader use today as a girls’ name, especially in the U.S., but parents are still using it for boys as well. Beverly. This Old English place name, which means “beaver stream,” was also originally used as a surname. From there it became a name that was used by both sexes as a first name. Today, if it’s used at all, it’s usually given to a girl.