From drip +‎ stone.

dripstone (plural dripstones)

1. (architecture) A protective moulding over a door or window that allows rain to drip away from the structure.

   Synonyms: hoodmold, headmold, throating, drip, watershoot

2. A water filter in which impurities are removed by running water through a porous stone.
3. (geology) Stalactites and stalagmites collectively.

• redpoints