| deep(noun, adjective, good, feeling, strong) |
| serious(adjective, hard, difficult, complex, deep) |
| esoteric(adjective, hard, easy, obscure, difficult) |
| difficult(adjective, hard, complex, thoughtful, intellectual) |
| hard(adjective, difficult, intense, complex, emotional) |
| intense(adjective, strong, great, complete, severe) |
| recondite(adjective, easy, obscure, deep, thoughtful) |
| weighty(adjective, hard, difficult, complex, thoughtful) |
| severe(adjective, hard, difficult, intense, complex) |
| knotty(adjective, hard, difficult, complex) |
| intricate(adjective, hard, difficult, complex) |
| involved(adjective, hard, difficult, complex) |
| tricky(adjective, hard, difficult, complex, cunning) |
| complex(adjective, hard, difficult, tedious, demanding) |
| laborious(adjective, hard, difficult, complex) |
| abstruse(noun, adjective, easy, obscure, difficult) |
| thorny(adjective, hard, difficult, complex) |
| arduous(adjective, hard, difficult, complex) |
| grave(adjective, hard, difficult, complex, greatness) |
| grievous(adjective, hard, difficult, complex) |