See nnnnnn's comment below.

The [NASA website][1], describing ['oumuamuam][2], uses the term "interstellar object." Extrasolar asteroid would seem to be another option.  I haven't seen a unique word different from asteroid that originated outside of the solar system.

It seems a simple prefix is sufficient to describe objects beyond the solar system, i.e. exoplanet.

Scienfitic American has an [article][3] which uses the term "interstellar object."

Also, see answers to:

 - [Is intrastellar commonly used by astronomers to refer to objects within our solar system?](https://astronomy.stackexchange.com/q/33680/7982)
 - [Adjective for things outside our solar system](https://astronomy.stackexchange.com/q/30131/7982)



  [1]: https://www.nasa.gov/feature/jpl/small-asteroid-or-comet-visits-from-beyond-the-solar-system
  [2]: https://en.wikipedia.org/wiki/%CA%BBOumuamua
  [3]: https://www.scientificamerican.com/article/two-interstellar-intruders-are-upending-astronomy/?utm_source=newsletter&utm_medium=email&utm_campaign=daily-digest&utm_content=link&utm_term=2019-11-27_featured-this-week&spMailingID=61644144&spUserID=MTE1NjM1NDM5MjAwS0&spJobID=1764375774&spReportId=MTc2NDM3NTc3NAS2