Tyga Loses $16k Legal Battle ... With His Accountant

Tyga gives new meaning to "rack, rack city" by racking up his accountant's credit card bill to the tune of $16k -- and now a judge has ordered him to pay the piper.

Accountant Robert Seltzer claims he and the rapper struck an oral agreement back in 2011 ... in which Tyga could use Robert's CC to charge food, hotel, and transportation while touring -- and then pay him back at the end of each month.

Problem is ... Tyga never paid, so he sued to get his money back -- $13,396, plus interest.

But Tyga missed his court date ... so a judge entered a default judgment in Robert's favor and ordered the rapper to cough up $16,801.67.