When you’re writing by hand, a hyphen and a dash can look pretty similar, although the meanings differ. You might throw in a hyphen to link two well-known words or add a dash—for impact, of course.

Once upon a time, “goodbye” was hyphenated. So was “teenager.” So was “email.” So were many other terms that we don’t hyphenate today. What happened? The same thing that happens to a lot of multiword ...