The meaning of the word "horst" (not capitalised so a common noun) can be found HERE.
However, you searched for the meaning of "Horst" (capitalised, so a proper noun/name). It's a surname mainly in Germany and The Netherlands and its origins are German.
I'm not really clear why you think it has anything to do with English.
The name is of Old High German origin, meaning "man from the forest", "bosk" or "brushwood". In modern German, "Horst" is also a translation of English aerie, the nest of an eagle or other bird.