| invisible(adjective, hard, knowledge, faint, subtle) |
| indistinct(adjective, dull, hard, weak, soft) |
| indiscernible(adjective, hard, knowledge, faint, subtle) |
| impalpable(adjective, hard, knowledge, fine, faint) |
| faint(adjective, calm, dull, quiet, weak) |
| intangible(adjective, knowledge, slight, fine, subtle) |
| slight(adjective, calm, dull, hard, weak) |
| obscure(adjective, weak, pale, subtle, hidden) |
| inaudible(adjective, dull, quiet, hard, weak) |
| vague(adjective, dull, hard, weak, soft) |
| ill-defined(adjective, weak, pale, insensible, faded) |
| inappreciable(adjective, hard, light, knowledge, slight) |
| subtle(adjective, hard, slight, fine, thin) |
| gentle(adjective, calm, dull, weak, soft) |
| indistinguishable(adjective, hard, knowledge, faint, subtle) |
| infinitesimal(adjective, hard, big, small, faint) |
| insensible(adjective, hard, knowledge, indifferent, faint) |
| minute(adjective, hard, soft, slight, gentle) |
| unclear(adjective, dull, quiet, weak, soft) |
| unnoticeable(adjective, hard, knowledge, faint) |