These have always seemed odd to me. In my experience, "major/minor" are not priorities but measures of scale, "trivial" is a measure of work, "blocker" is something else altogether. "Critical" might be a priority, but really is a measure of importance.
"Priorities" might instead be something like "critical, high, medium, low".
It seems "Scale" might be better fit for some of these, as an estimate of necessary work: "major, moderate, minor, trivial"