| burdensome(adjective, hard, difficult) |
| esoteric(adjective, hard, difficult) |
| inextricable(adjective, hard, difficult, complicated, complexity) |
| painful(adjective, hard, difficult) |
| tight(adjective, hard, difficult) |
| anfractuous(adjective, hard, difficult) |
| grinding(adjective, hard, difficult) |
| nasty(adjective, hard, difficult) |
| operose(adjective, hard, difficult) |
| tangly(adjective, hard, difficult) |
| weighty(adjective, hard, difficult) |
| impossible(adjective, hard, difficult, number) |
| precarious(adjective, hard, difficult) |
| troubled(adjective, upset, hard, difficult, anxious) |
| convoluted(adjective, hard, simple, fancy, difficult) |
| puzzling(adjective, hard, fancy, difficult, heavy) |
| perplexing(adjective, hard, fancy, difficult, delicate) |
| system(noun, entity, organization, form, order) |
| obscure(adjective, hard, difficult, delicate, heavy) |
| abstruse(noun, adjective, hard, fancy, difficult) |