"Full" in OCS?

Whilst reading through the text of Janachek's "Glagolitic Mass" I was
struck by how the line in the Latin mass:

"Pleni sunt coeli et terra gloria tua"

is translated as:

"Plna sut nebozem nja slavy tvojeje!"

Is this word "plna" an original Slavic word or a borrowing from Latin?

Sorry if this seems like a stupid question. I don't have access to an
OCS grammar or lexicon at the moment. When I'm in Moscow this summer I
hope to buy T.A. Ivanova's "Staroslavjanskij jazyk", which someone
told me is one of the best grammars for the language.

Christopher Culver