- A surname derived from several Old and Middle English words; also adopted by immigrants whose surnames began with a K.
- A male given name derived from the surnames, or from a rare medieval given name (as the Sir Kay of Arthurian legend), Welsh Cai, Latinized as Caius, related to the modern male name Kai.
- A short form of Katherine and other female names beginning with a "K"; popular as a middle name.
- 1970 Santha Rama Rau, The Adventureress, Harper&Row 1970, pages 99-100:
- She frowned at the girl's response. "Kay?" she said. "That is not a name. And what of your family?"
- "Catalina," the girl amended quickly. "I am used to being Kay at work. My family name is Gómez - we come from Mindanao, where we had pineapple plantations - "