A slender woman or girl, usually graceful and sometimes with the implication of sublime station over everyday people
Her heart fluttered with expectation---her step was buoyant with hope, and she sprung into the carriage with the lightness of a sylph. — Mary Brunton (1778-1818), Self-Control: A Novel.
Any one of several species of very brilliant South American humming birds, having a very long and deeply-forked tail; as, the blue-tailed sylph (Cynanthus cyanurus)