ar·got 
(ärgō)
(ärgō)n.
A specialized vocabulary or set of idioms used by a particular group: thieves' argot.
[French, from earlier argot, underworld of beggars and thieves, of unknown origin.]
Usage Note: The pronunciation of argot as (ärgət) was long considered acceptable and has historically been included in most dictionaries. However, it is falling out of favor; in our 2005 survey, 75 percent of the Usage Panel found that pronunciation unacceptable.