This is the 11079th most frequent Polish word.
gabinetu
"Gabinetu" means "of the office" or "of the study" (genitive form of "gabinet").
Here, "gabinetu" is in the genitive case indicating relation to "door" (possessive context).
Drzwi od gabinetu są zamknięte.
The door to the office is closed.
In this sentence, "gabinetu" is again in the genitive case to express location or relation to the office.
Nie mogę się doczekać wizyty w twoim gabinecie.
I can't wait for a visit to your office.
In this sentence, "gabinetu" is the genitive form of "gabinet" (office/room) used to indicate ownership or association with the dentist.