What is the meaning of "wafer" in this extract from The Great Gatsby by F. Scott Fitzgerald, chapter 3:
The caterwauling horns had reached a crescendo and I turned away and cut across the lawn toward home. I glanced back once. A wafer of a moon was shining over Gatsby’s house, making the night fine as before and surviving the laughter and the sound of his still glowing garden.
Does it mean only "disc"?