stalactite

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An icicle-shaped mineral deposit, usually calcite or aragonite, hanging from the roof of a cavern, formed from the dripping of mineral-rich water.

Century Dictionary and Cyclopedia

1. n. A deposit of carbonate of lime, usually resembling in form a huge icicle, which hangs from the roof of a cave or subterranean rock-opening, where it has been slowly formed by deposition from calcareous water trickling downward through cracks or openings in the rocks above. Water containing carbonic acid in solution, which it has gained in filtering through the overlying soil, has the power of dissolving carbonate of lime, which it deposits again upon evaporation; stalactites are hence common in regions of limestone rocks. They are sometimes white, and nearly transparent, showing the broad cleavage-surfaces of the calcite, as those of the cave near Matanzas in Cuba; but commonly they have a granular structure with concentric bands of pale-yellow to brown colors. In some caverns the stalactites are very numerous and large, and of great beauty in their endless variety of form, especially in connection with the stalagmites, the corresponding depositions accumulated beneath the stalactites upon the floor of the caverns. The caves of Adelsberg in Carniola and of Luray in Virginia are among the most celebrated for the beauty of their stalactites.
2. n. A similar form of some other mineral species, such as are occasionally observed, for example, of chalcedony, limonite, etc., but only sparingly and on a small scale.
3. n. A like form of lava sometimes observed in connection with volcanic outflows. Lava stalactites have been noted hanging from the roofs of lava caverns in the crater of Kilauea in Hawaii; and slender forms of a nearly uniform diameter of one fourth of an inch, and from a few inches to 20 or 30 inches in length, ornament the roofs of caverns in the lava stream which descended from Mauna Loa in the same island in 1881. Stalagmites of lava rise from the lava floor beneath.
4. n. In decorative architecture of certain schools, a pendent ornament with sharp edges and generally one of many in a group.

Wiktionary

1. n. geology A mineral deposit of calcium carbonate, in shapes similar to icicles, that hangs from the roof of a cave.

GNU Webster's 1913

1. n. 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. n. In an extended sense, any mineral or rock of similar form and origin.

WordNet 3.0

1. n. a cylinder of calcium carbonate hanging from the roof of a limestone cave