I use the term Scotch-Irish, which requires some explanation, judging from the nearly hysterical emails I receive from time to time.
Many people erroneously believe that the term means something along the lines of “mixed Scottish and Irish.” Not so. The Scotch-Irish were Scots who lived in Ireland. The term is similar to other ethnic and national combinations, such as German-American.
The Scots in Ireland were a well-defined ethnic group in the 17th and 18th centuries. They were (typically) descendants of lowland Scots who took up farms in northern Ireland during the Ulster Plantations. Their descendants in Ulster became the Irish Protestants, still at odds with the Irish Catholics. Today, they call themselves Ulster Scots. In America, the same group historically called themselves Scotch-Irish.
Some amateur scholars prefer the pedantic emendation Scottish-Irish, on the theory that contemporary Scots distinguish Scottish (themselves) from scotch (whisky). I can hold my own when it comes to academic silliness, but I can’t understand re-renaming an ethnic group to conform to modern notions of style, while disregarding both their historic and modern names for themselves. I prefer the historically correct Scotch-Irish to the artificial Scottish-Irish (and to the demographically correct Ulster Scots).