The name Sylveon/Nymphia derives from the word nymph. In Greek mythology there are 5 different types of nymph; water, land, plant, underworld and celestial nymphs, referring to flight. Since water, plant (grass) and underworld (dark) have been taken by other eeveelutions Sylveon represents either land or celestial nymphs, perhaps both. This explains why Sylveon is depicted as being etheral and feminine with wind blowing through her ribbons.
http://en.wikipedia.org/wiki/Apsara
Sylveon = Flying