Omnam is an adverb of affirmation and emphasis meaning "truly," "surely," or "indeed." It intensifies the truth-claim of a statement and appears in both confessional contexts (acknowledging God's justice) and dialogic contexts (affirming what is being said). Related to the root aman (to be faithful/true).
The adverb omnam connects to the great biblical theme of divine faithfulness. When Job and the Psalms use it, they are anchoring their speech in what is genuinely true rather than what is convenient or comforting. Truth-telling — even hard truth — is a form of worship. God is the God of amen (Isaiah 65:16), and His people are called to speak with the same integrity.