A prayer or a vow — the two meanings are deeply connected. A euche is a solemn declaration before God, whether a petition lifted upward or a commitment made in His presence. James uses it for the 'prayer of faith' that heals the sick; Acts uses it for Paul's Nazirite vow.
Euche binds prayer and vow together, revealing that authentic prayer is always covenantal. When we pray, we are not merely requesting — we are entering a sacred exchange with God. James 5:15 declares that the euche of faith will restore the sick — not because of the prayer's eloquence but because of God's faithfulness to His covenant people. The vow aspect reminds us that prayer carries weight; words before God are binding.