http://www.longmansec.com.eg/QuestAns.aspx?QA_ID=93
Some dictionaries — including
Longman Dictionary of Contemporary English Online and Merriam-Webster International Online — do not clearly distinguish these two words.
They use historic to mean "very old," and your students can do the same.
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<!--[endif]-->Some other references do distinguish them and do not accept
historic to mean "very old."
The Cambridge Guide to English Usage explains the words this way:
"
Historic is more self-consciously associated with the making of history, so that a
historic event is one which people feel is particularly significant in the life and culture of the nation.
Historical is more neutral, acknowledging that something belongs to the past, or to the study of the past, or else that it really happened and is not fictitious." (p 250)
Let’s look at some examples according to this distinction:
A historical book is a book about history, but a historic book is one that is particularly significant in the culture, perhaps because it was the first of its kind — the first novel, the first book printed rather than copied by hand, the first book to deal with a certain subject, etc.
A historical building is simply an old building. A historic building is considered important because a memorable event happened in or near it — an assassination, the signing of a treaty, the founding of an important organization, etc.
A historical person is one who really existed in the past. Legends are usually fantastic imaginary stories that grow around a historical figure. That is, the person really existed, even though the deeds and events of the legend are imaginary or exaggerated.
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Again, LDOCE uses
historic to mean "very old." In the cases of buildings or markets such as Khan El-Khalili that are described as "historic," it is not always clear whether only "very old" is meant or "historically significant." Your students can use
historic with these words. But for other things they should distinguish — a historical novel (a novel set against real events), a historical person (one who actually lived), etc.