| clever(adjective, sharp, smart, intelligent, cunning) |
| grinding(adjective, hard, difficult, complex, awkward) |
| labyrinthine(adjective, hard, difficult, complex, involved) |
| operose(adjective, hard, difficult, complex, awkward) |
| oppressive(adjective, hard, difficult, complex) |
| stressful(adjective, hard, difficult, complex) |
| ticklish(noun, adjective, understanding, hard, easy) |
| composite(adjective, hard, difficult, complex) |
| esoteric(adjective, hard, difficult, complex) |
| knotted(adjective, hard, difficult, complex) |
| treacherous(adjective, mean, smooth, wrong, fake) |
| trickish(adjective, hard, difficult, complex) |
| designing(adjective, mean, smooth, sharp, smart) |
| backbreaking(adjective, hard, difficult, complex, awkward) |
| byzantine(adjective, hard, difficult, complex, involved) |
| daedal(adjective, hard, difficult, complex, involved) |
| disturbing(adjective, hard, difficult, complex) |
| impossible(adjective, hard, difficult, complex) |
| nasty(adjective, hard, difficult, complex) |
| painful(adjective, hard, difficult, complex) |