Akin to the entry I posted about geographic vs geographical, the pair of words historic and historical also deserve a few comments. Is there a difference between the two? Yes, there is.
Historical refers to or relates to something having the character of history. In other words, it's an adjective that links a noun to something related to something that happened in the past. Examples: historical novels (novels based on events from the past); historical data (data collected from times past); historical perspective (a view on things from the eyes of people from the past).
Historic means a famous or important point in history. What I did last year isn't historic but Barak Obama getting elected as the first black president of the United States is historic. When you use this adjective, it means you are referring not only to something from the past, but something significant or important.
These are the distinct definitions of historic and historical. This is not to say that dictionaries don't make these two words share definitions. But the primary definitions are what I laid out here.
