If that is the case - if it is possible for it to be the case; i.e. whatever one is formally taught is deemed correct regardless, given that all words are made up and just a selection of letters; then what do you think the 'top' (of plug top) actually means?
Could, for example, a cup be called a 'cup top' just because someone formally teaches that?
Or can we not just say "Don't be so silly"?
I think we can probably agree that we both thing that it is a very silly term - because we expect the origin/derivation to be 'logical' and know what the word "top", alone means. hence, as you say, we therefore think that a 'plugtop' should be the top of a plug.
I think I have to bounce the question back at you, since I think we differ in our view of what is 'correct'(and hence what should be formally taught).
As you know, my inclination is to say that what is 'correct' at any point in time is the terminology that is, at that rime, in widespread and long-established 'common usage'. You, on the other hand, seem to feel that "widespread and long-established common usage" may be 'incorrect' and that the 'correct' terminology (which is what should be taught) is dictated by historical factors.
Having said that, "plugtop" is a very bad example of the general issue we so often discuss, since (in contrast with things like "light bulb" and "low voltage") the term is
not "in widespread common usage". I have rarely come across members of the general public using the term and, when they do, it is probably because they have seen it being used 'by the industry' and therefore think that it therefore must be 'correct'. For what it's worth, I've just asked a few family members what "plugtop" means, and none of them had a clue- other than suggesting that it might logically mean the top of some sort of plug (but without knowing whether that would be an 'electrical plug' or something else).
Despite the occasional use of the term, I can't recall ever having seen a product, or its packaging, labelled as a "plugtop",have you?
Kind Regards, John