standing stone

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

• noun A prehistoric monument of a class found chiefly in the British Isles and northern France, consisting of a single tall, upright megalith.

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

• noun A prehistoric monument consisting of an upright megalith; often in groups

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

• noun a tall upright megalith; found primarily in England and northern France