GEOCENTRIC is a 10 letter word that starts with G.

1. \Ge`o*cen"tric\, Geocentrical \Ge`o*cen"tric*al\, a.
   [Gr. ge`a, gh^, the earth + ke`ntron center: cf. F.
   g['e]ocentrique.] (Astron.)
   (a) Having reference to the earth as center; in relation to
       or seen from the earth, -- usually opposed to
       heliocentric, as seen from the sun; as, the geocentric
       longitude or latitude of a planet.
   (b) Having reference to the center of the earth.
   
   {Geocentric latitude} (of place) the angle included between
      the radius of the earth through the place and the plane of
      the equator, in distinction from geographic latitude. It
      is a little less than the geographic latitude.
   
   

2. \Ge`o*cen"tric\, Geocentrical \Ge`o*cen"tric*al\, a.
   ]
   Having, considering, or based on, the earth as center; as,
   the geocentric theory of the universe.