Worsted weight versus Medium weight yarn?

Question

Is there a difference? To the eye medium weight yarn looks a little heavier than worsted weight, but the way "worsted" was explained to me was that it was in between heavy and fine. So, if that is what worsted means, wouldn't that also mean medium? Just a little confused on yarn weights!!

Answer 1

what is a substitute for Lyon brands cupcake medium #4 worsted wt yarn?
Thank you.