1786, but in reference to the Wends; by 1844 as "native of Serbia," from Serbian Srb, perhaps from a root meaning "man." Serbian is attested from 1833 as an adjective, 1839 as a noun. More common in 19c. was Servian.
Entries linking to serb
Servian
1754 (n.), "a native or inhabitant of Servia," an old form of Serbia, which is the correct form; 1723 as an adjective, "pertaining or belonging to Servia or its inhabitants," from Medieval Latin Servia, from Serbian Serb (see Serb). The form is perhaps by confusion in Medieval Latin with servius. The English word formerly was sometimes extended loosely to Bosnians, Croatians, etc.
Serbian adj.
1833, from Serb + -ian. As a noun by 1839.
Serbo-
word-forming element meaning "Serbian, Serbian and," from Latinized combining form of Serb.