The Hebrew verb ud (עוּד) means to testify, to bear witness, to admonish, or to solemnly warn. It is used both in legal contexts (giving testimony) and in prophetic contexts (calling the people back to God with urgent warning). The word appears about 45 times in various stems throughout the Old Testament.
Ud captures the prophetic and covenantal function of bearing witness. When God 'testifies against' Israel, it is both a judicial declaration and a loving warning. The Levite cities of refuge required two or three witnesses (ud) to establish a matter, grounding this word in justice (Numbers 35:30). Nehemiah's reforms involved calling the people to account with solemn admonitions. The New Testament continues this function in the role of the Holy Spirit as the divine witness who testifies about Jesus (John 15:26) and convicts the world of sin.