СЕРЕБЬ / SEREB'

The Primary Chronicle mentions the tribe of Serbs as Серебь (Sereb'). The soft sign - Ь - as has been already explained, is the former 'i'. Thus, the true toponym's name should be SEREBI.

Serebi (სერები) is a purely Kartvelian plural form of a SERI noun.

Seri (სერი) is 'hill' in Kartvelian.

Hence, Serebi literally means 'hills'.

Now what we lack is an undoubtful connection between Serbs and hills. Here we go:

"...По прибытии на Балканы центрами поклонения стали холмы, особенно одинокостоящие. По сей день, многие холмы на побережье Далматии носят имя Перуна...".

"...Upon arriving at Balkans, the hills, especially lonely, became the centers of theolatry. Even today many hills on Dalmatian coast bear Perun's name...".
(article "Serbs from VII to IX century")

So, Serbia is a Kartvelian word too.

And to complete the story, 'seri' gave birth to Spanish 'sierra' too.