Meillet's law

Etymology
Named after the French Indo-Europeanist Antoine Meillet, who discovered it.

Proper noun

 * 1)  A Common Slavic accent law, according to which Slavic words have a circumflex on the root vowel (i.e. the first syllable) if that word had a mobile accent paradigm in Proto-Slavic and Proto-Balto-Slavic, regardless of whether the root had the Balto-Slavic acute register.