What is the X in X-mas?
Old English swift "moving quickly," related to swifan "move in a course, sweep" (see swivel). Related: Swiftly; swiftness.
type of bird (several species of the family Cypselidæ, resembling swallows), 1660s, from swift (adj.) in reference to its swift flight. Regarded as a bird of ill-omen, if not downright demonic, probably for its shrill cry. The name earlier had been given to several small fast lizards (1520s).