- immaterialHaving no matter or substance; incorporeal.
- impregnableOf a fortress or other fortified place: able to withstand all attacks; impenetrable, inconquerable, unvanquishable.
- imperturbableNot capable of being, or not easily, perturbed, excited, or upset; calm and collected, even under pressure.
- im-Expressing negation; not.
- imburseTo put into a purse; to save, to store up.
- impacableimplacable (unable to be appeased)
- impertransibleimpermeable