The Works of Dionysius the Areopagite, tr. by John Parker, [1897], at sacred-texts.com
For what reason all the Heavenly Beings, in common, are called Heavenly Powers.
Now that we have defined these things, it is worthy of consideration for what reason we are accustomed to call all the Angelic Beings together, p. 43 Heavenly Powers. For it is not possible to say, as we may of the Angels, that the Order of the holy Powers is last of all. The Orders of the superior Beings share in the saintly illumination. of the last; but the last in no wise of the first; and on this account all the Divine Minds are called Heavenly Powers, but never Seraphim and Thrones and Lordships. For the last do not enjoy the whole characteristics of the highest. For the Angels, and those above the Angels--Archangels, and Principalities, and Authorities,--placed by the Word of God after the Powers, are often in common called by us, in conjunction with the other holy Beings, Heavenly Powers.
But we affirm that, whilst often using the appellation, Heavenly Powers, for all in common, we do not introduce a sort of. confusion of the characteristics of each Order. But, inasmuch as all the Divine Minds, by the supermundane description given of them, are distributed into three,--into essence, and power, and energy,--when we speak of them all, or some of them, indiscriminately, as Heavenly Beings or Heavenly Powers, we must consider that we manifest those about whom we speak in a general way, from their essence or power severally. For we must not apply the superior characteristic of those holy Powers, whom we have already sufficiently distinguished, to the Beings which are entirely inferior to them, so as to overthrow the unconfused order of the Angelic ranks. For p. 44 according to the correct account which we have already frequently given, the superior Orders possess abundantly the sacred characteristics of the inferior, but the lowest do not possess the superior completeness of the more reverend, since the first-manifested illuminations are revealed to them, through the first Order, in proportion to their capacity.