Paul uses this extraordinary word in 2 Corinthians 9:15: "Thanks be to God for his inexpressible gift!" (anekdiegetos). Having spent the chapter urging generous giving and describing God's own generosity, Paul lands on a word that simply confesses the inadequacy of all language to capture what God has done in Christ. The gift of Jesus exceeds all description. It is the supreme answer to human poverty — a gift so vast it leaves the recipient speechless.
Anekdiegetos is formed from the alpha-privative (a = not) + ek (out) + diegeomai (describe/narrate in detail) — that which cannot be fully narrated, too great for adequate description. It appears only once in the New Testament.