| enigmatic(hard, obscure, sophisticated, tricky, complicated) |
| enigmatical(adjective, hard, tricky, complicated, caught) |
| entwined |
| fancy(adjective, hard, difficult, complex, sophisticated) |
| gasser(adjective, hard, fancy, difficult, complex) |
| hard(adjective, fancy, difficult, complex, sophisticated) |
| hard to explain(expression, adjective, hard, tricky, complicated) |
| hard to solve(expression, adjective, hard, tricky, complicated) |
| hi-tech(adjective, hard, fancy, difficult, complex) |
| hidden(hard, obscure, sophisticated, tricky, complicated) |
| hooked(verb, adjective, affected, concerned, occupied) |
| immersed |
| immersed in(expression, adjective, affected, concerned, occupied) |
| impaired(verb, hindered) |
| incriminated(affected, concerned, occupied, interested, implicated) |
| inextricable(adjective, complexity) |
| inhibited(verb, hindered) |
| interlaced(verb, adjective, hard, fancy, difficult) |
| interrupted(verb, hindered) |
| involuted |