WordNet (r) 3.0 (2006):

great circle
    n 1: a circular line on the surface of a sphere formed by
         intersecting it with a plane passing through the center

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "great circle":
   anklet, aphelion, apogee, armlet, astronomical longitude,
   autumnal equinox, band, belt, bracelet, celestial equator,
   celestial longitude, celestial meridian, cincture, cingulum,
   circle, collar, collarband, colures, earring, ecliptic, equator,
   equinoctial, equinoctial circle, equinoctial colure, equinox,
   fascia, fillet, finger ring, galactic longitude,
   geocentric longitude, geodetic longitude, girdle, girt, girth,
   heliocentric longitude, hoop, longitude, meridian, neckband,
   necklace, nose ring, orbit, perigee, perihelion, period, quoit,
   ring, small circle, solstitial colure, trajectory, vernal equinox,
   wristband, wristlet, zodiac, zone