The Greek adjective aneleēmōn means merciless, without mercy or compassion. It occurs only once in the NT (Romans 1:31) in Paul's list of vices that characterize those who have suppressed the truth about God and been given over to a debased mind.
Aneleēmōn in Romans 1:31 stands as the culmination of moral collapse: when a society has rejected God, mercilessness becomes a defining characteristic. This is the opposite of eleos (mercy) — one of God's most celebrated attributes. The contrast is stark: God is defined by mercy (Psalm 103:17; Lamentations 3:22–23), while those who reject Him become defined by its absence. Jesus' beatitude 'Blessed are the merciful, for they will be shown mercy' (Matthew 5:7) is the positive counterpart — those who know God's eleos become conduits of it.