Kerîythûth (כְּרִיתוּת) means divorce, cutting off, severance. From kārath (to cut). It refers specifically to the certificate of divorce mentioned in Mosaic law.
Deuteronomy 24:1,3: if a man finds 'something indecent' in his wife, he writes her a certificate of divorce. Isaiah 50:1 uses it theologically: 'Where is your mother's certificate of divorce with which I sent her away?' — God challenges Israel, declaring He never truly divorced His people. Jeremiah 3:8 says He gave faithless Israel a certificate of divorce, yet still calls her back. God's covenant faithfulness exceeds even the legal provisions for divorce. Jesus in Matthew 19:8 says Moses permitted divorce 'because your hearts were hard, but from the beginning it was not so.'