This is the 536th most frequent Japanese word.
室
"Room" or "chamber."
Here, 室 is used as a suffix to denote a specific type of room (library room in this case).
図書室にはたくさんの本があります。
The library room has many books.
In this example, 室 serves to indicate a room designated for a specific purpose (conference room).
会議室の予約をしました。
I booked the conference room.
Here, 室 indicates a room associated with a particular activity or function (music room).