Stalactite

Part of speech: noun (n.)

1. A pendent cone or cylinder of calcium carbonate resembling an icicle in form and mode of attachment. Stalactites are found depending from the roof or sides of caverns, and are produced by deposition from waters which have percolated through, and partially dissolved, the overlying limestone rocks.

2. In an extended sense, any mineral or rock of similar form and origin; as, a stalactite of lava.