Etymology
1. O.E.
cneo, cneow "knee," from P.Gmc.
*knewan (cf. O.N.
kne, O.Fris.
kni, M.Du.
cnie, O.H.G.
kniu), from PIE base
*g(e)neu- (cf. Skt.
janu, Avestan
znum, Hittite
genu "knee;" Gk.
gony "knee,"
gonia "corner, angle;" L.
genu "knee"). The verb meaning "to strike with the knee" is first recorded 1896. Phrase
knee-high to a grasshopper first recorded 1851 (earliest form was
knee-high to a toad, 1814).
Knee-deep is from 1535.
Knee-jerk (the patellar reflex) is a neurological phenomenon discovered and named 1876; the figurative use appeared soon after the phrase was coined.
Knee-slapper "funny joke" is from 1966.
2. Etymology tree
3. Proto-Indo-European *ǵnéw-der.
4. Proto-Indo-European *ǵnéwom
5. Proto-Germanic *knewą
6. Proto-West Germanic *kneu
7. Old English cnēo
8. Middle English kne
9. English knee
10. Inherited from Middle English kne, from Old English cnēow, from Proto-West Germanic *kneu, from Proto-Germanic *knewą, from Proto-Indo-European *ǵnéw-o-m, a thematic derivative of *ǵónu.
11. See also West Frisian knibbel, Low German Knee, Knie, Dutch knie, German Knie, Danish knæ, Norwegian Bokmål and Norwegian Nynorsk kne, Swedish knä; also Hittite 𒄀𒉡 (genu), Latin genū, Tocharian A kanweṃ (dual), Tocharian B kenī, Ancient Greek γόνυ (gónu, “knee”), γωνία (gōnía, “corner, angle”), Welsh glin (“knee”), Old Armenian ծունր (cunr), Avestan 𐬲𐬥𐬎𐬨 (žnum), Sanskrit जानु (jā́nu).
12. The obsolete plural kneen is from Middle English kneen, knen, kneon, kneuwene. See: Danish '
knæ', Swedish '
knä'.