Historic
Part of speech: adjective
Definition: having importance or significance in history belonging to the past; historical (see note below)
Example sentence: The high probability is if American forces withdraw from Afghanistan and if no alternative international arrangement is made that then the historic contests between the regions and the sects will reappear, the Taliban will re-emerge, and a very complicated and maybe chaotic situation will develop.
Past
Part of speech: adverb
Definition: in a direction that passes
Part of speech: preposition
Definition: beyond in place, quantity or time
Part of speech: noun
Definition: The period of time that has already happened, in contrast to the present and the future.The past tense.
Part of speech: adjective
Definition: Having already happened; in the past; finished.Relating to the past.(of a period of time) the one before this one
Example sentence: Change is the law of life. And those who look only to the past or present are certain to miss the future.