cotter pin

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

• noun A split cotter inserted through a hole or holes and bent at the ends to fasten two or more parts together.

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

• noun A split pin, the ends of which project through an object being fastened and are bent back to hold it in place

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

• noun a cotter consisting of a split pin that is secured (after passing through a hole) by splitting the ends apart