Dictionary.net

• A stone, often of great size and weight, resting upon another stone, and so exactly poised that it can be rocked, or slightly moved, with but little force.

2010 - New Age Dictionary Database
By Oddity Software

• A stone, often of great size and weight, resting upon another stone, and so exactly poised that it can be rocked, or slightly moved, with but little force.

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.