Douglas Harper's Etymology Dictionary
Usage examples of "moon-dog".
It took him a little while to get really used to them, though long before the Man had finished talking to Mew he was already trying to chase the moon-dog round the tower.
He was just beginning to get fixed by these first efforts, when the moon-dog dived down to the mountain-top and settled at the edge of the precipice at the foot of the walls.
The moon-dog would not tell him any more all the same: and if you ask me, I don't think he knew much about it.
The moon-dog said he had roamed all over the white side of the moon and knew it all by heart (he was very apt to exaggerate), but eventually he had to admit that the country seemed a bit strange.
The moon-dog did not know everything about the moon, as you see, or he would have known that this was the lair of the Great White Dragon — the one that was only half-afraid of the Man (and scarcely that when he was angry).