Definitions and usage
Historic: 1. momentous; 2. historically significant.
Historical: 1. of or relating to history; 2. of or relating to the past.
The words were originally synonyms—with historic developing second as a shortened historical—but they began to diverge in meaning around the 18th century, and the difference has solidified over time. They are still occasionally mixed up, but the differentiation is now so well-established that using one in place of the other is likely to strike many English speakers as wrong.
Buildings, villages, districts, and landmarks deemed historically important are often described as historic because they are historically significant in addition to being of or related to history. Societies dedicated to recognizing and preserving these things are called historical societies because they are concerned with history but not momentous in themselves.
Early morning parties were held across the city to mark the historic event. [CTV.ca]
That’s in addition to historic droughts and fires in Texas, record low temperatures in Seattle, and snow and flooding in the Midwest. [NPR]
Historical fiction is currently enjoying a tremendous renaissance, both in terms of literary and commercial recognition. [Guardian]
Optimism that stock prices will rise over the next six months remained below its historical average of 39% for the second consecutive week. [Forbes]
When we cut to the USS Arizona “a few minutes after eight”, the historical footage creates a narrative that is genuinely chilling. [Sydney Morning Herald]