noun
non-smoking room
A room where smoking is prohibited, typically found in hotels, restaurants, or public facilities.
禁煙室を予約したいのですが。
I'd like to reserve a non-smoking room.
このホテルには禁煙室が少ない。
This hotel has few non-smoking rooms.
喫煙室 is a smoking room, the opposite of 禁煙室.
Compound of 禁煙 (no smoking) and 室 (room).