[Grimm's law] n [Jacob Grimm] (1838): a statement in historical linguistics: Proto-Indo-European voiceless stops became Proto-Germanic voiceless fricatives (as in Greek pyr, treis, kardia compared with English fire, three, heart), Proto-Indo-European voiced stops became Proto-Germanic voiceless stops (as in Latin duo, genus compared with English two, kin), and Proto-Indo-European voiced aspirated stops became Proto-Germanic voiced fricatives (as in Sanskrit madhya "mid" compared with Old Norse mithr "mid")
GRIMM'S LAW
Meaning of GRIMM'S LAW in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012