STALACTITE

n. icicle-shaped mineral deposit hanging from the roof of a cavern

A stalactite (Greek stalaktites, (Σταλακτίτης), from the word for "drip" and meaning "that which drips") is a type of speleothem (secondary mineral) that hangs from the ceiling or wall of limestone caves. It is sometimes referred to as dripstone.
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Noun
1. a cylinder of calcium carbonate hanging from the roof of a limestone cave
(hypernym) cylinder
(part-holonym) cave
(substance-meronym) dripstone

n. stalactite, icicle-shaped mineral deposit hanging from the roof of a cavern

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

(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.