Shibboleth

Boyd’s Bible Dictionary:

(ear of corn, stream). Pronounced sibboleth by Ephraimites, and shibboleth by Gileadites. When the latter conquered the former, and held the fords of Jordan, they exacted the pronunciation of this word in order to distinguish friend from foe. Any other word beginning with sh would have answered the same purpose (Judg. 12:66Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame 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. (Judges 12:6)).

Concise Bible Dictionary:

A word chosen by the Gileadites—apparently without any reference to its signification, which some take to be “an ear of corn,” and others “a stream”—by which to ascertain those that were Ephraimites, who pronounced the SH as S, making the word SIBBOLETH. As the men fled from the victorious Jephthah and approached the ford of the river, they were thus tested, and the Ephraimites, who had brought the conflict on themselves, were slain (Judg. 12:66Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame 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. (Judges 12:6)). From this has originated the calling any watchword of a party, or indeed any particular view of truth or doctrine held by a section of the church, a mere “shibboleth.”

Jackson’s Dictionary of Scripture Proper Names:

an ear of corn: a flood: a branch