When the WHO named the “mu” variant in August, “nu” was next in line. But the WHO decided to skip it over because officials felt the letter was too similar to the English word “new,” which could have led to a bit of confusion. Then came “xi,” but the WHO also decided to nix it because it is the same as the common last name Xi and using it would violate the organization’s guidelines to name diseases. The WHO always seeks to “avoid causing offense to any cultural, social, national, regional, professional or ethnic groups,” the organization said in a statement.

The effort to avoid offending a large group of people is one of the main reasons why the WHO started naming variants after letters in the Greek alphabet. Before that, only the scientific name was used, which was confusing to regular people and often led to people referring to variants by the places where they were first detected. That practice was “stigmatizing and discriminatory,” the WHO said.