| incorporeal(abstract, theoretical, abstruse, philosophical) |
| indiscernible(obscure, dark, secret, unknown, hidden) |
| insoluble |
| insubstantial(abstract, theoretical, abstruse, philosophical) |
| intangible(intellectual, abstract, theoretical, abstruse, philosophical) |
| intellectual(sound, deep, rational, thoughtful, abstract) |
| interlaced(adjective, hard, fancy, difficult, complex) |
| inviolate |
| invisible(obscure, dark, deep, mysterious, unknown) |
| jesuitic(abstract, theoretical, abstruse, philosophical) |
| kabbalistic |
| lettered(knowledgeable, cultured, educated, erudite, enlightened) |
| literary(sound, knowledgeable, cultured, educated, erudite) |
| literate(knowledgeable, cultured, educated, erudite, enlightened) |
| loose |
| magical(obscure, strange, deep, mysterious, inexplicable) |
| mega factor(expression, adjective, hard, fancy, difficult) |
| metaphysical(adjective, physical, abstract, theoretical, presence) |
| mixed(adjective, hard, fancy, obscure, difficult) |
| mystery |