If you compiled a list of common Middle English words and their corresponding Modern English translations, how many entries would have been replaced by an etymologically distinct word in Modern English? It's difficult to Google, since I just get articles on the vocabulary changes from Old to Middle English, which is not what I want.
By 'common', I mean concepts you would expect people to have a word for in both eras, like go, hand or red, and by 'replace', whether the default word is a direct descendant of the Middle English word in both meaning and form or if it was replaced by another word, either native or loaned.
So, tongue would count as retained, since it existed with the same meaning and use in Middle English. While dog would be a replacement, since while hound exists today and dog existed then, dog is the default word now where hound was before.