The Aramaic verb aman means to be faithful, trustworthy, or reliable — equivalent to Hebrew aman (root of 'Amen'). In Daniel 6:4, it describes the faithfulness that distinguished Daniel from all his peers: those seeking charges against him found no corruption, for he was trustworthy.
When Daniel's enemies searched his conduct and found nothing — because he was aman — this became an extraordinary testimony to what covenant faithfulness looks like in exile. God's faithful servant is vindicated, just as the Hebrew root amen declares God's own trustworthiness. Daniel's faithfulness is a type of Christ, who was utterly without fault yet condemned — and then vindicated in resurrection. In both cases, faithfulness under pressure leads to vindication by God.