1) Immemorial is an adjective, meaning, something or someone that is too old, ancient, has existed or had existed too long ago, and is not memorated anymore, thus not commemorated in fact, what means not actually remembered or remained in memory anymore. For ex. immemorial posession, indicating posession of something by someone too long ago. Or also ex. 'immemorial usage'thus an object, or house immobile, that was used too long time ago, and is not used anymore. Or we can add immemorial event' thus a historical event, that has not remained, or not (also officially) commemorated, or someone, an immemorial hero of war for ex. that are not memorated anymore at national level, officially, from a nation.

2) Imminent is an adj. too, is direct, evident, unpredictable, thus we say, 'an imminent accident' meaning an accident that happened in an unpredictable way, suddenly on the street. -We also say, 'immient danger' a possible, direct danger for something likely to happen, thus possible, in an unpredictable way. For ex. 'some drugs are imminent threat for health, thus there is danger of dying after few times taken, being imminent for heart for ex. causing problems to heart, or threat generally for immunity system. etc, in the long run. Or we say 'danger for imminent accident' for ex. whn drivers drive too fast, and exceed limits of velocity, or drive under influence of alcohol, can cause accident imminently, thus danger for accident in a direct way.