Cowgill's law (Greek) explained

Cowgill's law says that a former pronounced as //o// vowel becomes pronounced as //u// between a resonant (pronounced as //r//, pronounced as //l//, pronounced as //m//, pronounced as //n//) and a labial consonant (including labiovelars), in either order. It is named after Indo-Europeanist Warren Cowgill.

Examples:

• el|νύξ 'night' < PIE (cf. la|nox, Vedic < *nakts, got|nahts, gen. sg. hit|nekuz)
• el|φύλλον 'leaf' < PIE (cf. la|folium)
• el|μύλη 'mill' < PIE (cf. la|molīna)
• el|ὄνυξ 'nail' (stem grk-x-proto|ónukh-) < early PG < PIE (cf. ang|nægl < PGerm )

Note that when a labiovelar adjoins an pronounced as //o// affected by Cowgill's law, the new pronounced as //u// will cause the labiovelar to lose its labial component (as in el|núks and el|ónuks/ónukh-, where the usual Greek change > has not occurred).

References

• Book: Sihler, Andrew L.. Andrew L. Sihler

. Andrew L. Sihler. New Comparative Grammar of Greek and Latin. Oxford University Press. 1995. 0-19-508345-8.