No definition of beauty has remained consistently accepted through the ages. The culture of a philosopher was always a strong influence on how esthetic concepts such as beauty were approached. In Western philosophy, the earliest attempts at a definition that have come down to us were in the writings of the Greek philosopher Plato about 2,500 years ago. For the next 2,500 years, the question was addressed from the shifting cultural perspectives of multiple philosophers, down to our own time of the 21st Century. Today's definitions still reflect the "ideal" concepts presented by Plato, as well as the "scientifically objective" concepts developed over the past 200 years. The fundamental difference between the "ideal" and "scientifically objective" concepts remains unresolved: Is beauty an inherent property not dependent on how it is perceived as Plato wrote, or is it a property very dependant on perception and comparison as it is defined "objectively"? Conceptions of the beauty of the human face and body have shifted over time and from different cultural perspectives, but a concept that has remained somewhat stable is that of "harmony of parts as seen in the whole"-for example, the "parts" of hair, forehead, eyes, nose, lips and chin when viewed in the whole make a beautiful face. An archetype of the "unity of parts" concept is the head of Aphrodite-the Classic Beauty-sculpted by the Greek artist Praxiteles 2,500 years ago (see http://artcyclopedia.com/artists/praxiteles.html.
In 21st Century terms, the definition most apt for beauty is that it has a high degree of esthetic value that may or may not include "prettiness", interwoven with powerful emotional elements such as pain, courage and fear. In painting and sculpture think of Michelangelo (see http://www.saintpetersbasilica.org/Altars/altars.htm), in music think of Beethoven as conveyers of beauty that stirs our deepest responses.
In contrast is the concept of "prettiness", an aesthetic concept often mistakenly taken as a synonym for beauty. Prettiness is an esthetic value that gives pleasure with no discordant elements such as pain or courage. A change of hairdo may be "pretty"; a popular song may be "pretty". The definition of beauty potentiated by courage and fear was perhaps in the mind of Ernest Hemingway when he wrote of the tragic beauty he saw in the bullring, in the bullfighter that faced the bull and possible death with courage overcoming fear-what Hemingway called "grace under pressure".
The Japanese artist Hokusai's "Great Wave" block print captures the fearsome power and beauty of nature in the enormous ocean wave breaking over three tiny boats where humans courageously fight to survive against almost overwhelming odds (see http://andreas.com/hokusai.html).