The Slavonic-Serbian language (славяносербскій / slavjanoserbskij or словенскій slovenskij; Serbian: славеносрпски / slavenosrpski) is a form of the Serbian language which was used, exclusively as a written language (no one ever actually spoke it), at the end of the 18th century and the beginning of the 19th century, predominantly by Serbian writers in Vojvodina and other parts of the Habsburg Monarchy. As such, it was also occasionally used in Montenegro and liberated Serbia in the early stages.
Taking a sentence from Zaharije Orfelin's Славеносербски магазин (The Slavonic-Serbian Magazine) as an example of the language could be useful:
Весьма бы мені пріскорбно было, ако бі я кадгод чуо, что ты, мой сыне, упао у пянство, роскошь, безчініе, і непотребное жітіе
(Latin: "Veśma by meni priskorbno bylo, ako bi ja kadgod čuo, čto ty, moj syne, upao u pianstvo, roskoš', bezčinie, i nepotrebnoe žitie").
Such a sentence shows that the language preserves old Slavic forms - thereby being similar to Russian, the most conservative of the Slavic languages - (čto instead of što), (roskoš' instead of raskoš), as well as the appearance of the letter –t in the third personplural of the present tense (oni mogut' instead of oni mogu). Furthermore, this language had no defined grammar, and it was used in a form that suited whoever used it.