| firm opinion(expression, idiom, belief) |
| flat(strong, certain, definite, resolved, unalterable) |
| for a fact(expression, idiom, clear, certain, definite) |
| free from doubt(expression, idiom, clear, certain, definite) |
| genuine(clear, certain, definite, unquestionable, undisputable) |
| going(strong, certain, definite, resolved, unalterable) |
| guaranteed(certain, unquestionable, undisputable) |
| hard |
| idle |
| impartial belief(expression, idiom, belief) |
| impartial opinion(expression, idiom, belief) |
| impassible(cold, indifferent, unyielding) |
| implicit belief(expression, idiom, belief) |
| implicit opinion(expression, idiom, belief) |
| incontestable(clear, certain, definite, unquestionable, undisputable) |
| incontrovertible(clear, certain, definite, unquestionable, undisputable) |
| indefatigable |
| indicating firmness(expression, idiom) |
| indisputable(clear, certain, definite, unquestionable, undisputable) |
| indubitable(clear, certain, definite, unquestionable, undisputable) |