| implausible(adjective, strange, fantastic, doubtful, dubious) |
| impracticable(adjective, wild, silly, foolish, unreasonable) |
| insane(adjective, silly, foolish, fantastic, unwise) |
| phantasmagoric(adjective, fantastic) |
| preposterous(adjective, happy, false, foolish, fantastic) |
| ridiculous(adjective, silly, foolish, fantastic, unwise) |
| silly(adjective, foolish, fantastic, practical, dreamy) |
| unlikely(adjective, strange, fantastic, doubtful, dubious) |
| unsubstantial(adjective, unreal) |
| wacky(silly, foolish, unwise, impractical) |
| brainless(impractical, half-baked, doomed) |
| fictitious |
| flat |
| gone(adjective, informal, practical, unlikely, idealistic) |
| imbecilic(impractical, half-baked, doomed) |
| in the clouds(expression, idiom) |
| mad(adjective, silly, foolish, unwise) |
| unactual(adjective, unreal) |
| unattainable(adjective, wild, unreasonable, useless, absurd) |
| unauthentic |