| eager(adjective, keen, energetic, enthusiastic, excited) |
| determined(adjective, success, interested, obsessed, promising) |
| difficult(adjective, hard, ability, complex, effort) |
| weighty(adjective, hard, difficult, importance, complex) |
| serious(adjective, hard, difficult, importance, complex) |
| severe(adjective, hard, ability, difficult, complex) |
| laborious(adjective, work, hard, difficult, complex) |
| hard(adjective, ability, difficult, complex, effort) |
| operose(adjective, work, hard, difficult, complex) |
| taxing(adjective, hard, difficult, complex) |
| toilsome(adjective, hard, difficult, complex) |
| trying(adjective, hard, difficult, complex) |
| arduous(adjective, hard, tough, ability, difficult) |
| burdensome(adjective, hard, difficult, complex) |
| complicated(adjective, hard, difficult, complex) |
| elaborate(adjective, hard, ability, difficult, complex) |
| problematic(adjective, hard, difficult, complex) |
| tough(adjective, hard, difficult, complex) |
| oppressive(adjective, hard, difficult, complex) |
| painful(adjective, hard, difficult, complex) |