A peculiar reflection in the sky, common in arctic regions, indicating the presence of open water beneath.(noun)
The Century Dictionary (Public Domain)
Use "water-sky" in a sentence
"Whenever the state of the air was favourable, the dark, heavy water-sky was visible in a marked degree, leaving no doubt that a large extent of Ross Sea was open the whole year round."
"The constantly increasing 'water-sky' to the north had long ago warned us that we were approaching the sea; the presence of the birds told us it was not far off."
"A dark water-sky hung over the Barrier on the west and north-west, showing that there was open sea off the mouth of the Bay of Whales."