The root behind faith, truth, faithfulness, and "Amen." In the Qal, it means "to support" or "to nurture"; in the Niphal, "to be faithful, reliable"; in the Hiphil, "to believe, trust." The word conveys firmness, reliability, and settled confidence.
When Genesis 15:6 says Abraham "believed" (he'emin) the LORD, it means he threw his full weight upon God's promise. This is not casual agreement but radical trust. The related noun emunah (faithfulness) describes the steadfast reliability of God. Our English word "Amen" comes directly from this root.
The Hebrew concept of faith bridges both testaments. Paul's quotation of Genesis 15:6 in Romans 4 makes Abraham's aman-type faith the prototype for Christian belief. The word family includes emunah, emeth (H571), and amen — faith, truth, and faithfulness are expressions of the same reality.