| imprimatur | A person's acceptance or guarantee that something is of a good standard | |
| impregnable | Not able to be defeated, overcome, or captured; very strong | |
| importune | To ask (someone) pressingly and persistently for or to do something | |
| imploring | To beg urgently or piteously, as for aid or mercy; beseech; entreat | |
| implication | The conclusion that can be drawn from something although it is not explicitly stated | |
| implacable | Unable to be placated or appeased | |
| impinge | To have an impact or effect, especially a negative one | |
| impetus | The force or energy with which a body moves | |
| imperious | Assuming power or authority without justification; arrogant and domineering | |
| imperative | Of vital importance; crucial | |