This section, taken from Memli Krasniqis publication “The roots of Balkan Wars (1912-1913):Serbian territorial claims toward lands inhabited by Albanians“, published 2014, has an interesting analysis:

“[…] Indeed, the ancient inhabitants of Attica, the old Athenians, with Kossyphos or “Kotyphos” called a black bird, which in Albanian language is known as “Mëllenjë”. The field of Blackbirds in the ancient Greek langauge was called “Kossyphopeidion”, which in translation means Field of Blackbirds, better known as Kosovo Field. The same meaning has the word Kos-Kosovi also in the Serbian language. Therefore, this toponym is not of Slavic origin, but derives from the ancient Greek language, and during the Middle Ages, the Serbs borrowed it from the local population, Roman-Byzantine culture and other religious institutions.”

According to this analysis, the name “Kosovo” is not of Serbian origin, but rather Greek-Byzantine.

Source: The roots of Balkan Wars (1912-1913):Serbian territorial claims toward lands inhabited by Albanians. 2014. Memli Krasniqi. Source here.