To be extremely lucky, to emerge from danger unscathed. The term probably was invented by Shakespeare, for whom charmed had the significance of “magical.” Thus Macbeth proclaims he is magically protected against death (“I bear a charmed life, which must not yield to one of woman born,” 5.7) but is nevertheless slain by Macduff, who “was from his mother’s womb untimely ripped.” The expression was transferred to less combative affairs and said of anyone who escaped unfortunate consequences. It was a cliché by the mid-nineteenth century.