snakestone

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A small stone or piece of porous substance reputed to cure snakebite.
2. n. See whetstone.

Century Dictionary and Cyclopedia

1. n. Same as ammonite: from an old popular notion that these shells were coiled snakes petrified.
2. n. A small rounded piece of stone, such as is often found among prehistoric and other antiquities, probably spindle-whorls or the like. Compare adder-stone.
3. n. A kind of hone or whetstone found in Scotland.
4. n. Same as serpent-stone, 1.

Wiktionary

1. n. A kind of hone slate or whetstone obtained in Scotland.
2. n. paleontology An ammonite (because of its coiled form).

GNU Webster's 1913

1. n. A kind of hone slate or whetstone obtained in Scotland.
2. n. (Paleon.) An ammonite; -- so called from its form, which resembles that of a coiled snake.