This is the 15797th most frequent Polish word.
sąsiednim
"Adjacent" or "neighboring."
In this sentence, 'sąsiednim' is used as an adjective describing the noun 'budynku'. It means 'neighboring' and describes the location of the building in relation to something else.
Mieszkam w sąsiednim budynku, więc mamy blisko.
I live in the neighboring building, so it's close.
Here, 'sąsiednim' modifies 'pokoju', meaning 'neighboring' or 'next', indicating proximity of the room.
W sąsiednim pokoju słychać dźwięki muzyki.
You can hear music sounds in the next room.
The word 'sąsiednim' describes 'mieście', indicating that the city is nearby or adjacent.