Antonio vs. Antonia. Gino vs. Gina. Mario vs. Maria. We’re used to -o endings pointing to male names and -a endings to female. But parents today want names that stand apart from the pack, with the potential to surprise us. For a growing number, that means flipping the script on final letters.

-A names like Ezra and Luca are now fast-rising hits for boys. Meanwhile parents of girls have been tiptoeing toward -o endings, starting with what I call “hidden o names.” These showcase the unconventional feminine -o sound but cushion the spelling with silent letters: Willow, Shiloh, Margot.

I first described the “hidden o” trend back in 2014. Since then the growth of hidden-o names has accelerated, so names like Monroe and Marlowe rank in the US top 1000. And in the past few years, the actual -o ending has started to join the party. Girls’ -o names are now at the point where hidden o’s were at the time of the original article.

Girls’ -o names surged once before, in the middle of the 20^th century. That spike was all about the nickname Jo, which singlehandedly accounted for three-quarters of the era’s -o girls. This time, no single name is taking the lead. The new -o surge is a phenomenon of pure sound, spread out across dozens of rare but rising names. They include:

• The few established English female -o names, like Cleo and Margo
• Contemporary English word names like Halo and Indigo.
• Names from other languages like Cielo (Spanish, “heaven/sky”) and Emiko (Japanese; multiple meanings depending on the kanji used)
• Nicknames from around the world like Lilo and Coco
• Names of female figures from classical mythology, like Juno and Echo

Notably, none of the top ten girls’ -o names are traditional male names. That suggests that the trend isn’t about sounding masculine per se. It’s more about staking out new fashion ground with names that capture attention.