🔼The word shibboleth in the Bible
The words שבלת (shibboleth) and סבלת (sibboleth) were used by the judge Jephthah and his men of Gilead to identify refugees from Ephraim who wanted to cross the Jordan from west to east (Judges 12:6).
The Ephraimites were asked to say שבלת but their dialect turned it into סבלת. We have of course no real idea how any of the Hebrew of the Bible sounded (there are no sound recordings of those days) and all we have is the written text.
🔼Etymology of the word shibboleth
The word שבלת (shibboleth) is a feminine noun meaning either a flowing stream or an ear of grain:
The word סבלת (sibboleth), on the other hand, doesn't otherwise exist. Some scholars (BDB Theological Dictionary) suppose that סבלת (sibboleth) is the Ephraimites' proper word for what the Gileadites called שבלת (shibboleth) but it might not be that simple.
The men of Gilead could have asked the Ephraimites to say anything, and they would have recognized their accent (like Peter was recognized to be from Galilee; Matthew 26:73). The men of Gilead called ears of grain שבלת, which means that they connected the growing of grain to the flowing of a river; it happened because it happened, not because anyone was doing anything about it (while obviously, in Gilead people also worked the land). The men of Ephraim, however, called grain סבלת, and that word derives from the verb סבל (sabal), meaning to bear or carry:
In other words, the difference between saying shibboleth and saying sibboleth is the difference between believing that you're getting somewhere because God leads you there and gives you what you need, and believing that you're getting somewhere because you're pulling your weight and you are providing for yourself and your people.
The word shibboleth reflects a flowing stream and a wealth of growing grain, while the word sibboleth reflects burdens, servitude and hardly ever enough.