and don't forget ox and bull!Are you saying that
ox and
bull are descended from PIE *
gwos? English
ox is usually considered to be from PIE *
uks-en- 'bull, ox'. Bull is from *
bhel- 'to blow, swell'.
Or, are you questioning the semantics of the root *
gwos? Historical linguists are doing two things when they reconstruct hypothetical PIE roots: first, the try for the sound of the word, and then, they try for a meaning. Etymological dictionaries use these two constructs without much commentary, but if you look at the literature, you'll see that what the roots (and meanings) are are a kind of shorthand for a bunch of data and ruminations on same. What is problematic with positing that a word for one age and sex of a
cow may change over the six or thousand years between PIE and English (or one of the other IE languages)? Words change in pronunciation and meaning all the time.