Other forms: wavily; wavier
If something is wavy, it's either very slightly curly, like your sister's wavy hair, or it has a surface or edge that curves back and forth, like the wavy corrugated metal on a barn roof.
Anything wavy is in some way composed of waves, whether it's your dog's wavy coat or the wavy surface of Lake Michigan. The adjective can describe an undulating movement or a still, static shape: "The wavy fries just taste better to me than the straight ones." Both wave and wavy stem from the Old English wagian, "to move to and fro."