orgy

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

• noun A social gathering involving unrestrained indulgence, especially sexual activity and drinking.
• noun Uncontrolled or immoderate indulgence in an activity.
• noun A secret rite in the cults of ancient Greek or Roman deities, typically involving frenzied singing, dancing, drinking, and sexual activity.

from The Century Dictionary.

• noun Secret rites or ceremonies connected with the worship of some of the deities of classical mythology, as the mysteries of Ceres; particularly, the revels at the festivals in honor of Dionysus or Bacchus, or the festival itself, which was celebrated with boisterous songs and dancing (see bacchante and mœmad): generally plural in this sense.
• noun Hence A wild or frantic revel; a nocturnal carousal; drunken revelry.
• noun Synonyms Revel, Debauch, etc. See carousal.

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

• noun A frantic revel; drunken revelry. See orgies
• noun A sacrifice accompanied by certain ceremonies in honor of some pagan deity; especially, the ceremonies observed by the Greeks and Romans in the worship of Dionysus, or Bacchus, which were characterized by wild and dissolute revelry. Usually in the plural form.
• noun Wild, drunken, or licentious revelry; an uninhibited carouse.
• noun A series of sexual activities involving more than two couples in a group.
• noun An event characterized by unrestrained indulgence in passion.

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

• noun A revel involving indiscriminate group sexual activity.
• noun Excessive indulgence in a specified activity.

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

• noun a wild gathering involving excessive drinking and promiscuity
• noun any act of immoderate indulgence
• noun secret rite in the cults of ancient Greek or Roman deities involving singing and dancing and drinking and sexual activity