ǵónu

The neuter u-stem noun *ǵónu ("knee") provides one of the most phonologically regular cognate sets in the IE body-part vocabulary. The initial palatal *ǵ- serves as a diagnostic for the centum-satem classification, while the u-stem inflection preserves an archaic nominal pattern. Latin genū ("knee") continues the form with centum treatment of *ǵ as g. Derivatives include genuflect ("to bend the knee"), and possibly genuine (genuīnus, if from the custom of a father acknowledging a newborn by placing it on his knee — though this etymology is debated). Greek góny (γόνυ) shows the same centum treatment. The derivative gonýpeton ("kneeling") appears in classical texts. The medical term genu- (as in genu varum, "bow-leg") derives from the Latin form. Sanskrit jā́nu ("knee") shows the regular satem shift *ǵ > j. The Avestan zānu confirms the Indo-Iranian development. Gothic kniu and Old English cnēow (Modern English knee, with silent k-) show the Germanic reflex with Grimm's Law: *ǵ > *g > *k. The preservation of the initial k- in English spelling, despite its loss in pronunciation, is a relic of the older pronunciation (the k was sounded in Middle English). Hittite genu ("knee") provides the earliest attestation, from the Anatolian branch. The direct correspondence Hittite genu : Latin genū : Greek góny constitutes one of the strongest pieces of evidence for the genetic unity of the Anatolian branch with the rest of Indo-European. Lithuanian kelỹs (from a different root, replacing the inherited form) shows that lexical replacement can affect even basic body-part vocabulary. Old Irish glún (from *ǵlū-no-) preserves a Celtic variant.