Bacchanalia

Bacchanalia \bak-uh-NAIL-yuh\ , noun;
1. Plural, capitalized: The ancient Roman festival in honor of Bacchus, celebrated with dancing, song and revelry
2. A riotous, boisterous, or drunken festivity; a revel

Well, being naked is a good start for revelry... (source)

This word dates to the 1630's as "drunken revelry" from the name of the Roman festival held in honor of Bacchus. Bacchus is the Roman version of Dionysus, who was the god of the grape harvest, winemaking, and wine, and of ritual madness and ecstasy in Greek mythology.

Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Tbursday, September 15
Etymologies come from the Oxford English Dictionary and/or Etymonline.com