ADVENTISTS, SECOND, members of religious bodies whose distinctive feature is a belief in the imminent physical return of Jesus Christ.  The first to bear the name were the followers of William Miller, and adherents have always been more numerous in America than in Europe.  There is a body of Seventh Day Adventists who observe the old Sabbath (Saturday) rather than the Christian Sunday.  They counsel abstemious habits, but set no time for the coming of Christ, and so are spared the perpetual disappointments that overtake the ordinary adventist.