Wiktionary
n. 1 The phase of the moon when it is wane. 2 The moon when it is waning.
Usage examples of "old moon".
In the near foreground was the cracked, pitted surface of a crater-bottom, scarred and broken by ages-old moon-quakes, fading into a horizon strangely near, made jagged by incredibly rugged crater walls.
Only the old moon would shine on serenely, the night wind would stir the grasses, and the wide earth would take its rest, even as it did aeons before we were, and will do aeons after we have been forgotten.
I saw the Old Moon with the New Moon in her arms, hovering above a row of poplars.
Applying a mild repulsion to this--which was itself quite a world, with its diameter of over three thousand miles, though evidently as cold and dead as the earth's old moon--they retarded their forward rush, knowing that the resulting motion towards Jupiter would be helped by the giant's pull.