some kind of water that rises from the ground to wet the earth; the exact picture (mist, an underground flow, or a rain cloud) is genuinely uncertain.
This word appears only twice in the whole Bible, and both times it names water that comes up to moisten dry ground. The trouble is that no one is sure what kind of water. In Genesis it is what waters the earth before rain has ever fallen; in Job it is part of a poem about how God makes rain. Because there is so little to go on, scholars have read it three different ways, and the old translation "mist" is only one of them.
One long-standing reading takes it as a swell of fresh water welling up from below the ground, an underground source that floods the surface. This fits the picture in Genesis of the earth being watered before it rained, and it became the favored view of the major dictionaries through the late twentieth century. A second reading takes it as a rain cloud, partly because the surrounding verses in both Genesis and Job are about rain, and partly because the old Jewish translations into Aramaic rendered it "cloud." A third reading keeps the traditional "mist" or "dew": a ground-level moisture that is neither rain from above nor a river on the surface.
What ties all three together is the basic idea the word carries: water appearing to wet the earth, rising rather than falling. Beyond that, the meaning is one of the harder puzzles in the Hebrew Bible, and an honest entry has to leave the question open rather than pick a winner.