1) mechanism for fastening a door, box, etc., that requires a key or combination
to open it
2) section of a canal or river within gates for raising or lowering the water level
3) mechanism for exploding the charge of a gun
4) fasten or shut up with or as with a lock
5) imprison (a person)
6) make or become rigidly fixed
7) (cause to) jam or catch
8) link; interlock
All of these definitions are helpful, because together they give us that sense of a great quantity of water being held back in reserve, then powerfully let loose.
SIDE NOTE: [Well, "all the high mountains under the entire heavens were covered" -- that kinda rules out the concept of just a localized flood, doesn't it?]
But if we read all of the Scriptures about the flood, including this verse in Genesis 7:19-20, we could reasonably conclude that it would have been possible for these flood waters to cover the earth to a depth of twenty feel above the highest mountains if these vast quantities of water were falling from above, and at the same time, "all the springs of the great deep burst forth" (Genesis 7:11). I mean, if the quantity of water which was falling from above the sky was anywhere near even half of the amount of water which our seas contain today, that is a lot of water! I am sure that people will still have more questions about the flood and that's fine, but aren't these things that Scripture says at least starting to look less like a fantasy and a bit more possible to you?
Wow. All that just to say that on the second day, God created the sky.