| incomprehensible(adjective, hard, knowledge, obscure, difficult) |
| deep(adjective, hard, complete, obscure, difficult) |
| impenetrable(adjective, hard, knowledge, obscure, difficult) |
| infinite(adjective, complete, deep, immense, incalculable) |
| inscrutable(adjective, knowledge, obscure, dark, strange) |
| mysterious(adjective, hard, obscure, dark, strange) |
| obscure(adjective, hard, difficult, solid, dark) |
| profound(adjective, hard, complete, obscure, difficult) |
| bottomless(adjective, deep, immense, infinite, boundless) |
| enigmatic(adjective, hard, obscure, difficult, solid) |
| immeasurable(adjective, deep, constant, size, abundant) |
| abstruse(adjective, hard, obscure, difficult, strange) |
| abysmal(adjective, complete, deep, extent, profound) |
| recondite(adjective, obscure, dark, uncertain, sophisticated) |
| unintelligible(adjective, hard, knowledge, obscure, difficult) |
| boundless(adjective, complete, immense, infinite, incalculable) |
| puzzling(adjective, obscure, dark, strange, sophisticated) |
| measureless(adjective, constant, abundant, endless, immense) |
| inexplicable(adjective, hard, obscure, difficult, solid) |
| arcane(adjective, obscure, difficult, solid, strange) |