“Horse” and “Car”
The English word horse derives from the Proto-Germanic *hrussą, with metathesis of the /r/ and /u/. This, in turn, derives from the Proto-Indo-European *ḱr̥s-ós, a nominal derivative of *ḱers- “to run”.
In Proto-Celtic, this became *karros, with the meaning “wagon”. Through Gaulish, this produced the Latin carrus, which, via Norman French, produced the English word car.
Another derivative of this PIE root was the verb form *ḱr̥s-é-ti, which produced the Latin currere “to run”, which is the source of the English words courier and current.
Surprisingly, cart is from a completely different root, despite having a similar sound and meaning to car. Cart derives from Old Norse kartr (wagon, cart), ultimately from Proto-Indo-European *gretH “to tie”. “Cradle” and “crate” are also from the same root.