Nat is a diminutive of Nathaniel, Nathan, or Natalie. Natalie was derived from the Latin Dies Natalis, which means "birthday". This name was traditionally given to girls born at Christmas, so the reference to the birthday of Jesus Christ is fairly obvious. Natalie is very popular in Russian and French speaking countries. Saint Natalie is thought to have been martyred for her love and devotion to her husband Aurelius in the 4th century.