I find it very interesting to note the migration of euphemisms, with the taboo subject taking up residence in a succession of words or phrases. A case in point is "God blind me" => "Gor Blimey" => "Blimey".

But for migration analagous to that of the Arctic Tern on has to consider our way of dealing, verbally, with the place for the disposal of our bodily wastes.
Even the Latin -"latrine" - refers (I think) to a washing or bathing place.
English monks in the Medieval period called it "the necessary" (and I wonder if this is the root of the Geordie {i.e. NE England} term "the Netty" for the same building?)

Certainly by the time of the Stuarts - and, I think much earlier - the term, "the privvy," (i.e. - a private place) had come into use - and continues to be used to this day, although decreasingly so, usually in reference to an earth- or pail-closet.
The invention of a system to carry excrementitious matter far away from its source by the use of water was called - reasonably enough - a "Water Closet," which very soon became "W/C". There was no great love of initialised abbreviation at that period, so the use of initials in this instance can only be for euphemistic reasons, I believe.

The Victorians found that term vulgar and started to use "lavatory," meaning washing-place - a reference, perhaps to the fact that the W/C was often to be found in the bathroom. "The Lav" became an acceptable euphemism for a long time, but in recent years has been altered even more obscurely into "the Loo." Only a very common person would refer to "the Lav," these days!

There is a whole raft of terms for such places that are provided for general, rather than family, use. "Public Convenience" is a favourite, although, again, "W/C" is also quite frequent, and also "Toilet" - especially in buildings that are frequented by the public, such as restaurants.

Of course, there are a whole range of other euphemisms to be found, which are either peculiar to a particular family, or are an attempt at whimsical humour by a business person. (E.g., "Guys" and "Dolls")

One wonders why it is deemed proper to be so coy about a totally natural and essential function of the body. It is, as I hope I have demonstrated above, not a modern bit of prudishness, no left-over from the Victorian era, but a very long standing need to hide this function.

Is it for the same reason that many animals dig holes to hide their excrement?