A sylph is a lovely, slim young woman or girl. You could describe a row of graceful ballerinas as sylphs. The 19th-century French ballet “La Sylphide” is thought to have led to the use of sylph to describe slender girls, especially ballet dancers. A slim, graceful woman or girl.In the occult philosophy of Paracelsus, a being that has air as its element. Sylph is a mythological air spirit.