monolith

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A large block of stone, especially one used in architecture or sculpture.
• noun Something, such as a column or monument, made from one large block of stone.
• noun Something suggestive of a large block of stone, as in immovability, massiveness, or uniformity.

from The Century Dictionary.

• noun A single stone; by extension, any structure or object in stone formed of a single piece: it may be an independent monument standing alone, as an Egyptian obelisk, or a menhir, or any part of a structure, as a column.

from the GNU version of the Collaborative International Dictionary of English.

• noun A single stone, especially one of large size, shaped into a pillar, statue, or monument.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A large single block of stone, used in architecture and sculpture.
• noun Anything massive, uniform and unmovable.
• noun chemistry A continuous stationary-phase cast as a homogeneous column in a single piece.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a single great stone (often in the form of a column or obelisk)