Beauty is the fact, quality or condition of being beautiful.
Beautiful is someone or something that is very good and pleasing to look at.
These are the definitions of Beauty and Beautiful according to Collins Cobuild English Language Dictionary. But it is an old saying that tells the simple truth:
in the eye of the beholder.
That is why the famous Romantic poet John Keats, however charming the thought, might not be necessarily right in saying that:
A thing of beauty is a joy forever:
Its loveliness increases; it will never
Pass into nothingness; but still will keep
A bower quiet for us, and a sleep
Full of sweet dreams, and health, and quiet breathing.
Extract from John Keats' epic poem, Endymion, 1818