As a feminine given name, Kat is derived from the Greek name Aikaterine (Αικατερίνη), which is the feminine form of the masculine name Aikaterinos (Αικατερινος). Aikaterinos is a Greek adaptation of the Latin name Catharina, which is derived from the Greek word katharos (καθαρός), meaning "pure" or "clean".
As a masculine given name, Kat is primarily used as a short form of the name Katniss, which was created by the American writer Suzanne Collins for her novel series The Hunger Games. Katniss is a combination of the words "kat" (a type of wild edible plant) and "niss" (a shortened form of the name Melissa).
In some cases, Kat can also be a short form of the names Katarzyna (Polish), Katerina (Russian), or Kateryna (Ukrainian), all of which are derived from the Greek name Aikaterine.