The Greek adjective akarpos (ἄκαρπος) means unfruitful, without fruit, or barren — composed of the alpha-privative and karpos (fruit). It describes spiritual or moral unproductiveness.
Jesus taught that the branch abiding in the vine bears much fruit (John 15:5). Akarpos is its opposite — the word choked by worldly cares (Matthew 13:22), or false teachers who are autumn trees without fruit (Jude 12). Genuine faith produces fruit; fruitlessness reveals a problem at the root. The Spirit's fruit (Galatians 5:22–23) marks the Spirit-filled life.