After forty years in the Wilderness, the Israelites arrived at Canaan, the land that had been promised to them, to discover that there were already people living there.
The Book of Judges describes, among other things, the slaughters that were required to command the Promised Land. Among them there was a battle of Joshua and the Gileadites with a people called the Ephraimites, which the Authorized Version describes:
"And the Gileadites took the passages of the Jordan before the Ephramites: and it was so, that when those Ephraimites which were escaped said, Let me go over: that the men of Gilead said unto him, Art thou an Efhraimite? If he said, Nay: Then they said unto him, Say now Shibboleth; and he said Sibboleth: for he could not frame how to pronounce it right. Then they took him and slew him at the passages of Jordan: and there fell at that time of the Ephraimites forty and two thousand."
Shibboleth in Hebrew meant "ear of grain." The word was meaningless to the Ephraimites, but their inability to pronounce it identified their ethnicity, and thus their vulnerability. So, in time, the word in English has come to mean variously, Merriam-Webster says, "a word or saying used by adherents of a party, sect, or belief and usually regarded by others as empty of real meaning," "a use of language regarded as distinctive of a particular group," and "a custom or usage regarded as distinguishing one group from others."
Thus a shibboleth is anything, however intrinsically trivial, that enables us to separate ourselves from people we would prefer to look down on.
The word popped into my mind as I followed yet another sterile online discussion about the word irregardless, with predictably uninformed comments that it is "not a word"* and a mark of the "uneducated."
It was the "uneducated" that caught my eye, because I too in my hot-blooded youth was an insufferable prig about language and what I understood to be "correct" usage. It took me a long time to understand that formal standard English is not the only English and that all the other Englishes serve perfectly well in their respective domains.
Sneering at the "uneducated" who use some nonstandard form of English, I realize, is a pathetic form of linguistic snobbery, no more noble or praiseworthy than any other form of snobbery. It is common among people, like me, who can not claim distinction by birth, wealth, physical beauty, or social status. A defective education about how language works is all we've got, so we have to work it.
I once thought to respond to such whingeing that no one cares about your language peeves. Now I think that there are indeed other people who care about your language peeves, but they are not worth caring about.
*Yes it is. It has a spelling, a pronunciation, an etymology, a history, and a widely understood meaning. It has been listed, though as casual or nonstandard, in dictionaries for decades, and if you complain about that, you betray a lack of understanding of how dictionaries work and how language works.