| hard to understand(expression, adjective, idiom, difficult, complex) |
| heartless(adjective, person, mean, feeling, cool) |
| heavy-handed(adjective, difficult, complex) |
| insensitive(adjective, person, mean, cool, tough) |
| knotted(adjective, difficult, complex) |
| lumpish(adjective, difficult, complex) |
| onerous(adjective, dull, great, tough, severe) |
| perplexed(adjective, difficult, complex) |
| rigorous(adjective, strong, tough, severe, rough) |
| sophisticated(adjective, difficult, complex, involved, complicated) |
| toilful(adjective, difficult, complex, awkward, demanding) |
| unbearable(adjective, difficult, complex) |
| daedal(adjective, difficult, complex, involved, complicated) |
| drudgery(noun, adjective, work, difficult, complex) |
| esoteric(adjective, difficult, complex) |
| fusty(adjective, difficult, complex, old, sour) |
| heartrending(adjective, difficult, complex) |
| impossible(adjective, difficult, complex) |
| precarious(adjective, difficult, complex) |
| sensitive(adjective, difficult, complex) |