Definition of "frostwork"

Frostwork keeps its place on the window within three feet of the stove all day in my chamber.

1888, H. Thoreau, Winter: From the Journal of Henry D. Thoreau, Houghton, Mifflin and Company, page 343

More delicate frostwork, this time in the form of hairlike needles of calcite, occurs near the Pearly Gates. Here, as in all caves under the jurisdiction of the National Park Service, you are asked not to touch or handle the cave formations.

1968, William Henry Matthews, A guide to the national parks: their landscape and geology, page 236