Grimm's law
sound shift in the Germanic languages in which PIE voiceless stops become fricatives, PIE voiced stops become voiceless and PIE voiced aspirated stops become voiced stops or fricatives
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A diagram of Grimm's law and Verner's law
Grimm's law, also known as the First Germanic Consonant Shift or First Germanic Sound Shift, is a set of sound laws describing the Proto-Indo-European (PIE) stop consonants as they developed in Proto-Germanic in the first millennium BCE, first discovered by Rasmus Rask but systematically put forward by Jacob Grimm. It establishes a set of regular correspondences between early Germanic stops and fricatives and stop consonants of certain other Indo-European languages.