An Etymological Dictionary of Astronomy and Astrophysics

1. The joint of the leg that allows for movement between the femur and tibia and is protected by the patella; the central area of the leg between the thigh and the lower leg.
   

2. Something resembling a bent knee, especially a rigid or braced angle between two framing members (Dictionary.com). → alpha element knee

Etymology (EN): M.E. kne; O.E. cneo, cneow “knee” (cognates: O.Norse kne, O.Sax. kneo, M.Du. cnie, Dutch knie, O.H.G. kniu, Ger. Knie; cf. Pers. zânu, as below.

Etymology (PE): Zânu “knee,” Mid.Pers. šnûg “knee;” Av. žnu- “knee;” cognates: Skt. jānu-, Hittite genu “knee;” Gk. gonu “knee,” gonia “corner, angle;” L. genu “knee;” O.E. cneo, as above; PIE *gnéwo-.

1. An instrument for cutting, consisting essentially of a thin, sharp-edged, metal blade fitted with a handle.
   

2. Any blade for cutting, as in a tool or machine (Dictionary.com).

Etymology (EN): M.E. knif; O.E. cnif, probably from O.N. knifr;
cf. M.L.G. knif, M.Du. cnijf, Ger. Kneif; of uncertain origin.

Etymology (PE): Kârd “knife,” from Mid.Pers. kârt “knife;” Av. karət- “to cut;” cf. Skt. kart- “to cut,”
karəta- “knife;” Proto-Ir. *kart- “to cut.”

The same as → Foucault knife-edge test.

See also: → knife; → edge; → test.

1. To perceive or understand as fact or truth; to apprehend clearly and with certainty.
   

2. To have established or fixed in the mind or memory (Dictionary.com).

Etymology (EN): M.E. knowen, knawen, from O.E. cnâwan, akin to O.H.G. bichnâan “to recognize,” L. gnoscere, noscere “to come to know,” Gk. gignoskein, Pers. šenâxtan, dânestan, as below.

Etymology (PE): Dânestan “to know;” Mid.Pers.
dânistan “to know;” variant šenâxtan, šenâs- “to recognize, to know” (Mid.Pers. šnâxtan, šnâs- “to know, recognize”);
O.Pers./Av. xšnā- “to know, learn, come to know, recognize;” cf. Skt. jñā- “to recognize, know,” jānāti “he knows;” Gk. gignoskein “to know, think, judge,” cognate with L. gnoscere, noscere “to come to know” (Fr. connaître; Sp. conocer); P.Gmc. *knoeanan; O.E. cnawan, E. know, as above; Rus. znat “to know;” PIE base *gno- “to know.”

1. Acquaintance with facts, truths, or principles, as from study or investigation.
   

2. All the information, facts, truths, and principles learned throughout time.
   

Etymology (EN): M.E. cnawlece, from O.E. cnawan, cf. O.H.G. bi-chnaan, ir-chnaan “to know;” cognate with Pers. šenâxt, as below.

Etymology (PE): 1) Šenâxt, past stem of šenâxtan, šenâsidan “to know, discern, distinguish, be acquainted with;”
Mid.Pers. šnâxtan, šnâs- “to know, recognize,” dânestan “to know;” O.Pers./Av. xšnā- “to know, learn, come to know, recognize;”
cf. Skt. jñā- “to recognize, know,” jānāti “he knows;” Gk. gignoskein “to know, think, judge;” L. gnoscere, noscere “to come to know” (Fr. connaître; Sp. conocer); O.E. cnawan; E. know; Rus. znat “to know;” PIE base *gno- “to know.”

2. Dânestgân, literally “body of (what is) known,” from dânest, short for dâneste “known,” p.p. of dânestan variant of šenâxtan, as above,

• -gân suffix forming plural entities.

The thin layer of → vapor immediately adjacent to an irradiated surface. The thickness of the Knudsen layer is generally recognized to be in the order of a few → mean free paths from the surface.

See also: Named after Danish physicist Martin Knudsen (1871-1949); → layer.