An Etymological Dictionary of the German Language/Knie
Knie, n., ‘knee,’ from MidHG. knie, kniu (gen. knies, kniewes), OHG. chniu, chneo (gen. chnëwes, chniwes), n., ‘knee’; comp. Du. knie, f., AS. cneó (gen. cneowes), n., MidE. cnee, E. knee; Goth. kniu (gen. kniwis), n., ‘knee’; a common O. and ModTeut. word with the prim. meaning ‘knee,’ which also belongs to the allied Aryan words; genu-, gonu-, gnu- are the Aryan stems of the word; comp. Lat. genu, Gr. γόνυ (comp. γνυ-πετεῖν, γνύξ, ἰγνύαλ), Sans. iŭnu, n., ‘knee’ (abhijñu, ‘down to the knee,’ jñu-bãdh, ‘kneeling’). This Aryan stem gnu had when declined the variant gnew-, which appears extended in Teut. by the a of the a-declension, Goth. kniwa-. The shorter Teut. form knu-, Aryan gnu-, has been retained in Goth. *knu-ssus (inferred from knussjan, ‘to kneel’), ‘kneeling’ (the suffix -ssus is current in Goth.), and probably also in OIc. knúe, m., ‘knuckle’ (presupposing Goth. *knuwa, m.); there are also some abnormal l-derivatives, MidE. cnélien, E. to kneel, Du. knielen, and Swiss chnüle, ‘to kneel.’