| massy(adjective, hard, difficult, complex) |
| punishing(adjective, hard, difficult, complex) |
| toilsome(adjective, hard, difficult, complex) |
| arduous(adjective, hard, difficult, complex) |
| heavyweight(adjective, hard, difficult, complex) |
| grievous(adjective, hard, difficult, complex) |
| gloomy(adjective, dull, obscure, dark, heavy) |
| listless(adjective, action, dull, quiet, weak) |
| torpid(adjective, dull, quiet, weak, easy) |
| languid(adjective, action, dull, weak, easy) |
| dreary(adjective, gray) |
| slow(adjective, dull, weak, easy, relaxed) |
| ashen(adjective, dull, soft, obscure, lead) |
| inert(adjective, dull, quiet, weak, moving) |
| dingy(adjective, dull, soft, obscure, lead) |
| lackadaisical(adjective, action, dull, quiet, weak) |
| lethargic(adjective, dull, quiet, weak, easy) |
| lifeless(adjective, dull, soft, obscure, flat) |
| boring(adjective, dull, flat, lifeless, dreary) |
| dense(adjective, heavy, gloomy, gray, overcast) |