From a (as a negative particle) and karpos; barren (literally or figuratively) -- without fruit, unfruitful.
see GREEK a
see GREEK karpos
1. properly: δένδρα, Jude 1:12.
2. metaphorically, not yielding what it ought to yield, (A. V. unfruitful): Matthew 13:22; Mark 4:19; destitute of good deeds, Titus 3:14; 2 Peter 1:8; contributing nothing to the instruction, improvement, comfort, of others, 1 Corinthians 14:14; by litotes pernicious, Ephesians 5:11 (Wis. 15:4; cf. Grimm on Wis. 1:11).