Beauty signifies something more than a high degree of prettiness because ‘pretty’ and ‘beautiful’ can differ by category. We say “beauty is only skin-deep” but ‘beautiful’ can also describe character, what a person does and why. On the other hand ‘pretty’ can only be skin deep.
There’s nothing new here; the ancient Greeks thought phenotype and virtue were correlative (and that’s just one place to start). And/But in the eye of the beholder we maintain our postmodern pluralistic relativity. Your pretty/beautiful is valid but may not be my pretty/beautiful. We judge character and attractiveness differently according to our individual peculiar standards and we get them just as confused as love and lust.
Even so: embedded underneath the details of our glossy, high-res, gendered, digital standards of ideal faces and bodies – I think we really believe “beauty is as beauty does.”