| oppressive(adjective, hard, difficult, complex) |
| thorny(adjective, hard, difficult, complex) |
| taxing(adjective, hard, difficult, complex, laborious) |
| tight(adjective, hard, difficult, complex) |
| elaborate(adjective, hard, difficult, complex, exertion) |
| intricate(adjective, hard, difficult, complex, awkward) |
| leaden(adjective, hard, difficult, complex) |
| profound(adjective, hard, difficult, complex) |
| weighty(adjective, hard, difficult, complex) |
| ambitious(adjective, hard, difficult, complex) |
| grave(adjective, hard, difficult, complex) |
| grievous(adjective, hard, difficult, complex) |
| hefty(adjective, hard, difficult, complex) |
| knotted(adjective, hard, difficult, complex) |
| ponderous(adjective, hard, difficult, complex) |
| problematic(adjective, hard, difficult, complex) |
| serious(adjective, hard, difficult, harsh, cruel) |
| toilful(adjective, hard, difficult, complex, awkward) |
| disturbing(adjective, hard, difficult, complex) |
| involved(adjective, hard, difficult, complex, awkward) |