Willowy comes from willow (Old English welig, the willow tree) + the adjective-forming suffix -y, giving willowy (like a willow); modern English willowy means slender and graceful. In current use it is an adjective meaning "gracefully tall, slender, and lithe, often used to describe a person's physique". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The surface form is compositional: its joined elements remain visible in the modern word. The word's history is thus visible in its construction: the components remain interpretable even after the whole expression has settled into a conventional English meaning.