Think of things that count as one set. The clearest modern picture is a door in a bedroom wall: open it and your own bathroom is there, so the two rooms are not two separate places but one unit you have to yourself. Everything on this page is that idea seen from a different angle. Describe the small room and you get an en suite bathroom; describe the big one and you get a bedroom that is en suite; point at either as a thing and en suite becomes a noun. The older use drops the door altogether and keeps only the set: a hat and gloves made en suite belong together because they match, not because they touch.
The source records only that the phrase was taken straight from French en suite; it is used in English as one unit, with neither word carrying the meaning on its own.
來源資料只記錄一件事：這個說法是直接從法文 en suite 借進英文的。它在英文裡整組使用，en 和 suite 不會各自拆開表達這個意思。除此之外，資料沒有給更多來歷，所以這裡也不多推測。
Wiktionary entry for 'en suite' (etymology field: 'From French en suite'), kaikki extract in the supplied evidence packet
One branch
臥室連著自己的浴室
這一組就是核心畫面本身：兩個空間被一扇門連成一套。四個用法的差別只在你從哪邊講、以及當形容詞還是名詞用。
adjective · B2
Used before 'bathroom', 'shower' or 'toilet' to say that it opens straight off a bedroom and belongs to that room, instead of standing out in a hallway where several rooms share it.
（浴室）與臥室相連的