The Greek adjective dyskolos means hard or difficult — originally used of difficult-to-please people (literally 'hard with food'), it came to mean generally troublesome or hard. In the New Testament it appears famously in Jesus' teaching about wealth and the kingdom.
Jesus uses dyskolos in Mark 10:24 — 'How hard (dyskolos) it is to enter the kingdom of God!' — in the context of the rich young ruler. The accumulation of wealth creates a spiritual difficulty not of external compulsion but of inner attachment and trust. Where one's treasure is, there the heart will be also. The disciples' astonishment at Jesus' words reveals how counterintuitive the kingdom economy truly is.