Grimm's Law Definition

The statement of a series of systematic prehistoric changes of reconstructed Indo-European consonants to Proto-Germanic consonants: these hypothesized prehistoric sound shifts are reflected by consonant correspondences between Germanic words and their cognates in non-Germanic Indo-European languages: (1) IE voiceless stops (p, t, k) = Gmc voiceless fricatives (f, , h); hence, L pater (cf. paternal) = E father, L tenuis (cf. tenuous) = E thin, Gr kardia (cf. cardiac) = E heart (2) IE voiced stops (b, d, g) = Gmc voiceless stops (p, t, k); hence, L bucca (cf. buccal) = OE pohha, a sack, L decem (cf. decimal) = E ten, L genu (cf. genuflect) = E knee, which has lost the (k) sound (3) IE voiced aspirated stops (b + h, d + h, g + h) = Gmc voiced stops (b, d, g); hence, Sans bhrtar = E brother, Sans mādhu, honey = E mead, IE *ghostis = E guest These correspondences show the kinship, stressed in the etymologies of this dictionary, between various native English words and the English words borrowed from any of the non-Germanic Indo-European languages.

(linguistics) A sound change that affected the Proto-Indo-European stop consonants in the development of Proto-Germanic, causing devoicing or change into a fricative.