The Spanish correr, “to run” seems completely unrelated to the English horse. Looks can be deceiving.
Correr comes from the Latin for the same, currere. Currere, in turn, comes from the Proto-Indo-European root *kurs, which also means, “to run” — just like horse does! Both have the same common ancestor.
The weird thing is: how did the PIE *kurs turn into horse, they sound so different.
The explanation is that, in the Germanic languages like English, the k- sound turned into the h- sound. But in Spanish, the original k- sound remained, although usually written with a c-.
This explains many parallel words that have c- and h- sounds that map to each other between Spanish and English, like heart/corazon and head/cabeza.