I have always defined Ceilidh music as house party music from what ever instruments are at hand. I suppose, and it is hirrific to think so, that you could have a Ceilidh of nothing but accordions. Spoons, a fiddle or two, a whistle, and an old cheese crate to pound upon with a piano or guitar for chords would certainly fill the bill under my unscholarly definition.

As to the rest of you question there are many more qualified people in the forum that I who will be glad to help you with your definition.

Don