alternate spellings: Sylpheel, Shilfiel, Sylfeel, Sylfeer
The name "Sylphiel" (pronounced as silf-ee-ell in the dub) does not seem to have any specific origins. One conclusion I reached is that it could be derived from the Latin name 'Sylvia', meaning, "forest".
However, I believe that Sylphiel is derived from 'Sylph', -- which are imaginary beings who inhabit the air and are known to be very helpful to humans -- this is possibly where Sylphiel's humanitarian nature comes from. Another possibility is the 'Sylvan', a species of fairies that originated in Greece that are said to lure human males to their death in the woods. 'Sylvan' has also come to mean to abound in trees or have characteristics of the forest, which could symbolize Sylphiel's bond with Flagoon.
Sylphiel's name in Japanese is written in Katakana. This alphabet is used to write words that are not Japanese in origin. Reading left to right, the first character is "Shi". By itself, "Shi" means "Intent" in Japanese. The second character is "Ru" and the third character is "Fu", which means "Lotus" when translated. The small "i" follows with the last character being "Ru" again. There are no characters for the "L"s in her name because "R" and "L" sound almost exactly the same and are often used interchangeably. All together, this name would be pronounced "Shi-ru-fu-i-ru". Try saying it aloud; it is how the Japanese pronounce "Sylphiel".
Also, her name according to Kabalarians gives the following meaning. While Kabalarians just kinda makes up name meanings behind the names given, it's still cool to read them (especially when they're semi-accurate as you will see with Sylphiel's analysis).
The name of Sylphiel creates an overly-sensitive nature which causes you to sense and feel far more than you can understand or put into words. You have a deep, artistic, and creative side, which shows through a love for music and literature. Writing is a more natural mode of expression for your deeper thoughts and feelings than the spoken word. You have an ability to concentrate and work intently on anything, which holds your interest. However, you prefer to avoid routine, monotony, and mental tasks. You enjoy the out-of-doors and find your greatest peace and relaxation from the beauty and harmony of nature. You prefer to limit your friendships and associations to those who share your interests and appreciate your quiet, refined ways. Others often find it difficult to understand you. Your feelings tend to build up within you and, if you cannot release them through a creative, constructive channel, you could suffer with frustration, moods, and much inner turmoil. This name causes tension in the region of the solar plexus, as well as the heart and lungs. Health problems would center in those areas of the body.