Boukólos rule


The boukólos rule is a phonological rule of the Proto-Indo-European language. It states that a labiovelar stop dissimilates to an ordinary velar stop next to the vowel u or its corresponding glide w.
The rule is named after an example, the Ancient Greek word βουκόλος "cowherd", ultimately from Proto-Indo-European gʷou-kolos, dissimilated from gʷou-'kʷolos. If the labiovelar had not undergone dissimilation, the word should have turned out as *, as in the analogously constructed αἰπόλος "goatherd" < ai-kʷ'olos. The same dissimilated form gʷou-kolos is the ancestor of Proto-Celtic bou-koli-, the source of Welsh bugail and Irish buachaill, which is the common word for "boy" in the modern language.
Another example could be the Greek negation οὐκ, which Warren Cowgill has interpreted as coming from pre-Greek *ojukid < h₂oju kʷid, meaning approximately "not on your life". Without the boukólos rule, the result would have been *οὐτ.
The rule is also found in Germanic, mainly in verbs, where labiovelars are delabialised by the epenthetic -u- inserted before syllabic resonants: