Did you know that the words ‘milonga’ and ‘bailongo’ both refer to a place where people dance? Bailar is the Spanish verb meaning to dance. Bailongo is a lunfardo word.

Lunfardo is an argot (ie a secret language/slang in French, Spanish & Catalan). It was developed at the end of the 19th century and beginning of the 20th century by people from the various less wealthy socio-economic groups in and around Buenos Aires and Montevideo possibly to prevent outsiders from understanding their conversations.

Refs:

http://www.planet-tango.com/lyrics/elchoclo.htm & http://en.wikipedia.org/wiki/Lunfardo