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.
-ian
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.