Many linguists argue that there is one room in a house that has no name in English. Every name we give it, historically and now, is a euphemism. A common modern euphemism for the room is "rest room". I'm amused when such rooms are called bathrooms even when they don't have a bath. 

2 minutes ago, drpaladin said:

It could be called a reading room.

Even without books 

The word euphemism comes from the Greek word euphēmismos, meaning "use of auspicious words" or "avoidance of words of ill-omen," (from eu, "good", and phēmi, "I say"), reflecting its meaning of using words that are considered positive or less harsh.  The concept of euphemism is ancient, with the Athenians, for example, referring to the Erinyes (Furies) as the "Eumenides" or "kindly ones" to avoid calling them by their ill-omened name.

According to the Oxford English Dictionary (OED), the earliest known use of the noun euphemism in English dates back to the mid-1600s, specifically 1656, in the writings of antiquary and lexicographer Thomas Blount in his book, Glossographia. 

Examples of euphemism: 
* "My grandmother passed away peacefully in her sleep," is a common euphemism for saying someone died. 
* When a child asks, "Are you feeling sick?", a parent might say, "No, I'm just a little under the weather," which is a euphemism for being ill. 
* When a child asks, "Are you feeling sick?", a parent might say, "No, I'm just a little under the weather," which is a euphemism for being ill. 
* "We had to let him go due to budget cuts" is a euphemism for "we fired him".  
* The politician used the euphemism "collateral damage" to describe the accidental deaths of civilians. 
* Instead of saying the company is struggling financially, the CEO opted for the euphemism "negative cash flow".

9 minutes ago, drpaladin said:

Did some linguists miss lavatory?

My understanding is that the origin of lavatory is from Latin lavare "to wash" 

52 minutes ago, drpaladin said:

Did some linguists miss lavatory?

Thanks to Mirriam-Webster I could add that the use of lavatorium in Medieval Latin (again from lavare) suggests that even in Medieval Rome they used a euphemism for the room. 

31 minutes ago, drpaladin said:

For another euphemism, the necessary room.

Or we could call it the inhouse  

Of course there are many rural areas in Australia where the euphemism is outhouse.

19 minutes ago, Paladin said:

Of course there are many rural areas in Australia where the euphemism is outhouse.

An outhouse would indicate that the facility is located outside of the building or house.  But some older folks might refer to it as the privy.  A navy man might used the term "head" to refer to such a facility, while other military men may call it the "latrine". 

10 minutes ago, Bill W said:

An outhouse would indicate that the facility is located outside of the building or house.  But some older folks might refer to it as the privy.  A navy man might used the term "head" to refer to such a facility, while other military men may call it the "latrine". 

Indeed it was located outside of and usually away from the house. This was in unsewered areas and the contents of the pan when it was collected and taken away was referred to, euphemistically, as "night soil". There was also an implied threat of redbacks lurking in the outhouse or, dangerously, under the seat. 

"Head" is an interesting and specifically naval euphemism. Originally on sailing ships, it indicated where the "facility" (another euphemism) was located, and the term persists with modern day sailors, even though the facility is located elsewhere.  

Just the facts:

EUPHEMISM Definition & Meaning - Merriam-Webster

EUPHEMISM Synonyms: 33 Similar and Opposite Words | Merriam-Webster Thesaurus

(B.L.T.N.)