Octave is, in the ecclesiastical calendar, the period intervening between any of the higher festivals and the eighth day therefrom. The whole of this interval was formerly observed with great solemnity; and the Church of England has retained the notion by directing that the "preface" proper to Christmas- day, Easter-day, Ascension-day, and Whit-Sunday shall be used for the seven days immediately following each of these festivals; except that in the latter case (Whit-Sunday), that preface is to be used for six days only, because the eighth day from it is Trinity Sunday, which has a preface peculiar to itself. Sparrow, on the Common Prayer, says, because our whole life is the revolution .of seven days, the eighth or octave signifies eternity, and this was the mystical reason why octaves were annexed to festivals. Di Cange says, because our Lord rose on the eighth day (including Sunday to Sunday), the octave of the feast was the day on which the whole solemnity closed. See Riddle, Christian Antiquities, p. 677, 683.