Pūpū is the name for marine and land shells, such as pūpū ō Niʻihau: Niʻihau shells. It is also the Hawaiian word for appetizers, and that is how we most often hear it used.
Hōkū means "star," and is often used in names such as Hōkūleʻa, the star of gladness, or Nā Hōkū, the local recording industry awards program. Be sure to include the stresses, for it takes on a different meaning if you do not.