All this talk about wheels and horses on the Log makes it a good time to look at *éḱwos, the Proto-Indo-European word for "horse". Ringe says it's apparently unanalyzable, but Watkins suggests it can be segmented *eḱw-o-, "a suffixed form akin to the lengthened o-grade adjective *ōḱu-, swift".
*éḱwos became Latin equus, then equine, equestrian. In Greek, *éḱwos apparently became ἵππος hippos, but this is problematic because the appearance of initial /h/ and the change from *e- to i- are unexplained. Greek ἵππος is found in words such as hippopotamus, Hippocrene... and Philip, from φίλιππος philippos "fond of horses", from the combining form φιλο- philo- (from φιλέω phileō "to love") plus ἵππος.
In Valis, Philip K. Dick gives himself the pseudonym "Horselover Fat": Philip "lover of horses", and Dick, German for "fat".
In Old English, *éḱwos became eoh, which subsequently disappeared. The word horse has cognates in other Germanic languages, but it's thought to be of non-Indo-European origin - altho the OED mentions a theory that it's connected to Latin currere "to run".
In Italic languages, equus was supplanted by caballus (cheval, cavallo, etc), but the feminine form equa survived in Anglo-Norman ive "mare".