Meaning of Verner's law

Ver'ner's law'

Pronunciation: [key]
— Ling. Ling.
  1. the statement by K. Verner of a regularity behind some apparent exceptions in the Germanic languages to Grimm's law, namely, that Proto-Germanic voiceless fricatives became voiced when between voiced sounds if the immediately preceding vowel was not accented in Proto-Indo-European.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.