| impassive | Not feeling or showing emotion | |
| impeccable | In accordance with the highest standards; faultless | |
| impecunious | Having little or no money; penniless; poor | |
| impeded | Delay or prevent (someone or something) by obstructing them; hinder. | |
| impenetrable | Impossible to pass through or enter | |
| imperative | Of vital importance; crucial | |
| imperious | Assuming power or authority without justification; arrogant and domineering | |
| impetus | The force or energy with which a body moves | |
| impinge | To have an impact or effect, especially a negative one | |
| implacable | Unable to be placated or appeased | |