| abstract(hard, delicate, complex, tricky, complicated) |
| baffling(hard, delicate, complex, tricky, complicated) |
| confounding(hard, difficult, delicate, complex, tricky) |
| confusing(hard, difficult, delicate, complex, tricky) |
| deep(hard, delicate, complex, tricky, complicated) |
| difficult(adjective, hard, striking, tricky, complicated) |
| enigmatical(hard, difficult, delicate, complex, tricky) |
| entangled(hard, tricky, complicated, caught, multiplex) |
| esoteric(hard, delicate, complex, tricky, complicated) |
| formidable(hard, delicate, complex, tricky, complicated) |
| hard to solve(expression, idiom, hard, delicate, complex) |
| intricate(hard, tricky, complicated, caught, multiplex) |
| involved(hard, tricky, complicated, caught, multiplex) |
| loose(hard, delicate, complex, tricky, complicated) |
| mystical(hard, delicate, complex, tricky, complicated) |
| mystifying(hard, delicate, complex, tricky, complicated) |
| paradoxical(hard, difficult, delicate, complex, tricky) |
| problematical(hard, delicate, complex, tricky, complicated) |
| profound(hard, delicate, complex, tricky, complicated) |
| subtle(hard, delicate, complex, tricky, complicated) |