> That explains *(h)ékWos > híppos, because the */kW/ phoneme
> precedes a back vowel (*/o/). It also explains e.g. *kWis >
> tis 'who'.
Correction: the IE form does *not* have a true labiovelar in 'horse',
but rather a cluster /kw/. So the correct form is *(h)ékwos.
However, /Kw/ and /KW/ (where 'K' stands for any member of the velar
series) had come to be treated as the same before the classical Greek
dialects.