If someone's tall, slender, and graceful, you can describe them as willowy. Your willowy friend might prefer hip-hop, but she is as lithe and elegant as a ballet dancer.
When a person is willowy, they're as long, lean, and flexible as the branch of a willow tree blowing in the breeze. This adjective was first used in this way around 1790 — earlier, it meant "shaded or bordered by willow trees." And in the 17th century, before willowy was coined, the now-obsolete willowish was used to mean "the color of willow leaves."