I asked my grandmother about that when I was a child because I was confused. She lived on a large farm which originally was a cotton plantation before the Civil War and the house was built in 1849.
The early house, before plumbing, had a large "out house"...with separate areas for men and
women. Outside each was a small covered niche with a basin for washing hands afterwards.
However, the house had a large room inside for "Resting"....a Victorian euphemism for using the
toilet. This was used during winter or bad weather instead of the "outhouse." The room had a
commode that opened into a chair with a hole...and a porcelian bowl underneath which could be
emptied. This "Resting Room" was also used for bathing, since there was a large tub hidden inside
a closet which could be pulled out and had privacy curtains. It had a pipe leading outside the
house for emptying the tub water (the water still had to be brought up to fill the tub since there
was no plumbing as yet). When it was used for bathing it was called the "Bathing Room" and when
used for relieving one's self...it was called the "Resting Room."
Eventually I guess the terms were combined and it became the "Bathroom."
In the early 1900's, the house was wired for gas lighting and electricity, and plumbing installed. A
large room on the 2nd floor was fitted with a flush toilet and a small matching wash basin...and a
bathtub with running water was installed. I remember seeing both the toilet and basin as a child,
and the toilet was a pull chain "Crapper" model with a white porcelian bowl with blue, pink and
green flower designs inside. There was a matching wash basin...quite beautiful. The tub was a
large, deep, claw-foot model with a large brass gas water heater hanging over the tub which you had to light to heat the water a little before taking a bath.
At the time this "all-in-one" room was installed with both bathing and toilet facilities, and again due
to hold-over conventions of the earlier Victorian Era...until the 1920's this room was still called the
"Resting Room." Probably the origin of todays term "Restroom."
But, because it was also a "Bathing Room", these terms probably became merged at some point and
eventually became the "Bathroom"...meaning both facilities.
Each bedroom still had a large "bathing sink" (a mirror hung above on the wall) with a commode
or cabinet underneath, with it all standing upon a marble bathing area so that the wood flooring
would not get wet. Hidden within the commode/cabinate was a "potty" for use during the night.
The house still has the sinks in each bedroom, but the potties are no longer used since additional bathrooms with a toilet have been installed on the two upper floors.