This is described by Robert Chapman, in his Dictionary of American Slang, as ‘an amiable form of address’, the equivalent of ‘friend’ in an expression like ‘How you doin’, cousin?’ Like ‘friend’...

The first name of the aunt concerned normally follows this term in direct address, especially when young nephews and nieces are using it. As they become adults they are more likely to use ‘aunt’ on its own, or to make use of the first name....

Terms which indicate a relationship once removed, a great-aunt being the aunt of one’s father or mother. The ‘great-’ translates French grand, which is used for similar purposes in words like grandpère, grandmère,...

This occurs in the literature of the seventeenth, eighteenth and nineteenth centuries, used to the speaker’s niece, but modern examples are very difficult to find. Usage seems to have died away as with many other terms of family relationship....

A cousin in English kinship terminology is a relative with whom one shares a common grandparent or more distant ancestor, and who is not in one's own line of descent. The term cousin never applies where there are other specific terms to describe...