Stang's law

Stang's law is a Proto-Indo-European phonological rule named after the Norwegian linguist Christian Stang.

Overview

The law governs the word-final sequences of a vowel, followed by a semivowel or a laryngeal, followed by a nasal. According to the law these sequences are simplified such that laryngeals and semivowels are dropped, with compensatory lengthening of a preceding vowel.
This rule is usually cited in more restricted form as: *Vwm > *Vːm and *Vh₂m > *Vːm.
Often the rules *Vmm > *Vːm and also *Vyi > *Vːy are added:

PIE *dyéwm 'sky' > *dyḗm > Sanskrit, acc. sg. of, Latin diem, Greek Ζῆν, acc. of Ζεύς
PIE *gʷowm 'cow' > *gʷōm > Sanskrit, acc. sg. of, Greek βών, acc. sg. of βοῦς 'cow'
acc. sg. of PIE 'house' is *dṓm, not **dómm̥.
acc. sg. of PIE 'grain' after laryngeal colouring is the disyllabic *dʰoHnā́m, not trisyllabic **dʰoHnáh₂m̥ > **dʰoHnā́m̥