| difficult(adjective, difficulty, characteristics, toughness, characteristic) |
| hard(adjective, difficulty, characteristics, toughness, feature) |
| intricate(adjective, characteristic, feature, quality, aspect) |
| labored(adjective, feature, characteristic, quality, difficulty) |
| onerous(adjective, difficulty, toughness, feature, characteristic) |
| problematic(adjective, feature, quality, aspect, characteristic) |
| toilful(adjective, feature, characteristic, quality, difficulty) |
| toilsome(adjective, feature, characteristic, quality, difficulty) |
| troublesome(adjective, difficulty, characteristic, quality, problem) |
| complicated(adjective, feature, quality, aspect, characteristic) |
| tricky(adjective, feature, quality, aspect, characteristic) |
| baffling(adjective, problem, feature, characteristic, quality) |
| complex(adjective, characteristic, difficulty, situation, problem) |
| grueling(adjective, characteristic, difficulty, description, characteristics) |
| gruelling(adjective, characteristic, difficulty, description, characteristics) |
| involved(adjective, characteristic, difficulty, situation, problem) |
| laborious(adjective, characteristic, difficulty, description, characteristics) |
| problem(adjective, feature, quality, aspect) |
| severe(adjective, characteristic, difficulty, description, characteristics) |
| thorny(adjective, problem, feature, characteristic, quality) |