utopia

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

• noun An ideally perfect place, especially in its social, political, and moral aspects.
• noun A work of fiction describing a utopia.
• noun An impractical, idealistic scheme for social and political reform.

from The Century Dictionary.

• noun An imaginary island, described by Sir Thomas More in a work entitled “Utopia,” published in 1516, as enjoying the utmost perfection in law, politics, etc. Hence [lowercase] A place or state of ideal perfection.
• noun Any imaginary region.
• noun In entomology, a genus of coleopterous insects.

from the GNU version of the Collaborative International Dictionary of English.

• noun An imaginary island, represented by Sir Thomas More, in a work called Utopia, as enjoying the greatest perfection in politics, laws, and the like. See Utopia, in the Dictionary of Noted Names in Fiction.
• noun Hence, any place or state of ideal perfection.

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

• noun A world in which everything and everyone works in perfect harmony.

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

• noun ideally perfect state; especially in its social and political and moral aspects
• noun an imaginary place considered to be perfect or ideal
• noun a work of fiction describing a utopia
• noun a book written by Sir Thomas More (1516) describing the perfect society on an imaginary island