Americans who have wandered chilly London hallways in the middle of the night in search of a toilet will appreciate learning the peculiar British meaning of the word “ensuite.”
In French, a set of two rooms or more forming a single accommodation can be advertised as rooms en suite (forming a suite). But the single word French word ensuite means something entirely different: “then, later.” Around the middle of the 20th century English landlords and hoteliers began to anglicize the phrase, placing it before the noun, so that traditional “rooms en suite” became “en suite rooms,” Ads read “bath ensuite” or “toilet ensuite” as if the phrase meant “in the suite.” The phrase “en suite” came to be used solely to designate bathrooms attached to a bedroom.
Following standard English patterns, they hyphenated the phrase as “en-suite bath” and often made the phrase into a single word: “ensuite bath.” These have become standard British usage, but hoteliers often go a step further by writing “all rooms ensuite” (Americans would write “all rooms with bath”).
It is clearly nonstandard to use “ensuite” as if it were a noun synonymous with “toilet” or “bathroom”: “I went to the ensuite to take a shower.” You may puke on your suit, but not into “the ensuite.”