Shibboleth

Judges 12:6
Listen from:
(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. 12:6).