Many thanks for your fast response and encouragement. Sorry for bafflying you. 
 
 Linguistics is just a hobby of mine. At first I want to understand definitions linguists give to the various terms they use. I understand their definition of a dialect as a language spoken within geographical boundaries meaning that all englishmen and all americans speak a dialect but a different one. This definition of Dialect agrees neither with the Websters nor the common definition. The Websters is known. As for the common understanding of the word, to tell an inhabitant of Oxford or Paris that he's speaking a dialect could well be considered an insult. Either I'm overlooking something, the linguists themselves have constructed their own dialect redefining words from ours or the definition is just crazy.