A hanging, tapering piece of ice formed by the freezing of dripping water.
It's true. My upstairs neighbor had the heat up so high, that icicles constantly grew on the side of our roof for months. One day we heard about 200 pounds of ice fall at once and it knocked the railing right off of the staircase below.
I was driving my soft-top car under trees with long icicles hanging down. Thousands of them. It was all very beautiful in the light of the car headlights. Then one fell. It passed through the roof of the car and smashed into a thousand shards on the gear housing... But it could have entered my head.... !!!
Is isvand synonymous with istapp? Or are they only called istapper when they come falling down?
So in Peer Gynt they actually speak Danish? Or is it one of the many Norwegian dialects? "Isvand i blodet!", the Mountain King says at the end of his song.
Peer Gynt was written in what was essentially Danish by a Norwegian author, yes. At that time, there was a struggle between the proponents of the traditional Dano-Norwegian written language, and those who wanted a Norwegian written language that more closely resembled the way people actually spoke in Norway.
While Ibsen's writing was quite conservative, he did use Norwegian words in his writing as well, and eventually came to support Riksmål which you could say was a Norwegianised form of Danish at the time. Landsmål was the more radical variant.