homocyclic

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

• adjective Containing a closed ring structure made of only one kind of atom. Benzene, for example, is a homocyclic compound, having a ring consisting of six carbon atoms.

from The Century Dictionary.

• Having the same or only one circle or cycle.
• noun A closed-chain compound in which the ring consists only of carbon atoms, as benzene.

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

• adjective chemistry describing a cyclic system in which all the atoms of the ring are of the same element

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

• adjective containing a closed ring of atoms of the same kind especially carbon atoms