Kaywinnet Lee Frye was a character in the television show, Firefly, and it's movie sequel, Serenity. She was commonly known by the nickname Kaylee. She was the ship's mechanic. Kaylee was sleeping with the Serenity's mechanic, who could not fix Serenity. When Kaylee showed Captain Reynolds that the ship could be fixed, he gave her the mechanic's job. She was in love with Simon Tam.
The name appears to have been invented by Joss Whedon. It could be a combination of Kay, and the surname Winnett. Kay is a short form of Katherine, which means 'pure'. The surname Winnett is derived from Winthrop, which comes from winn, meaning 'friend' and prop, which means settlement. So, a possible meaning could be 'pure friend'.
Kaywinnet has never appeared in the Social Security Administration's name database.