rotaxane

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

• noun A complex molecule containing one or more macrocyclic ring components encircling a rodlike component that has end groups large enough to prevent the molecule from dissociating into its component parts.

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

• noun chemistry any complex of two molecules, one of which has the form of a ring, the other having the form of a rod, passing through the ring, and having end-groups too large to pass through the ring