Many English words have a very doubtful ancestry, but there is no doubt whatsoever concerning the etymology of the word ‘Pleb’. What is at issue here is usage in English / English. I would strongly caution anyone against calling any English person a pleb ~ in English / English pleb is a very bad word.
As recently as 2012 a very senior politician was forced to resign after a scandal when he was accused of calling policeman ‘plebs’. The fact that the politician in question also swore at the police officers, using foul language, was of little import when put against the mere suspicion that the Member of Parliament concerned had called the policemen ‘plebs’. There is even a name for this scandal ~ plebgate. (This is funnier than you may think, but you would have to know London to really get the joke.)
As it turned out, the word ‘pleb’ was never used in this case. The policeman lied. Had the word actually been used, then that politician’s career would have been over for ever.
In English / English today, ‘Pleb’ means someone of low social status, unsophisticated and uncultured, a common no account person who will never amount to anything, a person to despise and denigrate… The dictionary definition of ‘pleb’ says an ordinary person… Not in England. In England ‘pleb’ implies someone who is maybe one step up from a street drunk. Pleb is an extremely derogatory term in English / English.
Like many English words, ‘Pleb’ is of Latin origin, (most Latin words have roots in classical Greek). A pleb was an ordinary citizen of Rome ~ as opposed to a patrician, who was a nobleman and a member of the ruling classes. To call a man ‘patrician’ is today still something of a compliment. To call someone a pleb is, and always has been, an insult.
In the USA, a derivation of ‘pleb’ ~ plebe is a perfectly acceptable term for a cadet or freshman. Just don’t try calling an Englishman a plebe, not unless you want a smack in the gob, (mouth).
Honestly, in England you would often be better off saying ‘Eff Off’ (or words to that effect), or using the ‘C’ word than calling someone a pleb. Fuck-off, or the ‘C’ word is merely foul and uneducated language. Pleb is a calculated insult with cultural and class overtones. That applies doubly so if you are in any way cultured or educated, and the person to whom you are speaking actually is ‘lower class’.
Trust me, in English / English, ‘Pleb’ is a forbidden word.
Next time I’ll discuss the term Brass Monkey.