It's from Fisherman's Soul by Oscar Wilde:
'And we tarried for a moon, and when the moon was waning, I wearied and wandered away through the streets of the city and came to the garden of its god.
Could the above for a moon be understood as for a month?
In dictionary moon has a meaning for a month.
I think in this case the above moon is just a 'moon' in physical sense, not meaning any period of time.
I am teaching English literature, but English is not my native tongue.