The Collaborative International Dictionary of English v.0.48:

Eyeball \Eye"ball`\, n.
   The ball or globe of the eye.
   [1913 Webster]

WordNet (r) 3.0 (2006):

eyeball
    n 1: the ball-shaped capsule containing the vertebrate eye [syn:
         eyeball, orb]
    v 1: look at [syn: eye, eyeball]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "eyeball":
   baby blues, banjo eyes, be vigilant, be watchful, bright eyes,
   clear eyes, cornea, eye, eyelid, follow, gaze at, goggle eyes,
   have a looksee, hold in view, iris, keep in sight, keep in view,
   keep under observation, lens, lid, look after, look at, look on,
   look upon, naked eye, nictitating membrane, observe, ocular,
   oculus, ophthalmic, optic, optic nerve, orb, organ of vision,
   peeper, popeyes, pupil, reconnoiter, regard, retina, saucer eyes,
   sclera, scout, scrutinize, seeing, spy upon, starry orbs,
   unaided eye, view, visible, visual, visual organ, watch