The Collaborative International Dictionary of English v.0.48:

Optics \Op"tics\, n. [Cf. F. optique, L. optice, Gr. ? (sc. ?).
   See Optic.]
   That branch of physical science which treats of the nature
   and properties of light, the laws of its modification by
   opaque and transparent bodies, and the phenomena of vision.
   [1913 Webster]

WordNet (r) 3.0 (2006):

optics
    n 1: the branch of physics that studies the physical properties
         of light
    2: optical properties; "the optics of a telescope"

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "optics":
   Newtonian physics, acoustics, actinology, actinometry, aerophysics,
   applied physics, astrophysics, basic conductor physics, biophysics,
   catoptrics, chemical physics, cryogenics, crystallography,
   cytophysics, dioptrics, electron optics, electron physics,
   electronics, electrophysics, geometrical optics, geophysics,
   heliography, heliology, heliometry, infrared spectroscopy,
   macrophysics, mathematical physics, mechanics, medicophysics,
   microphysics, microscopics, microscopy, natural philosophy,
   natural science, nuclear physics, optical physics, optometry,
   philosophy, photics, photography, photology, photometry, physic,
   physical chemistry, physical optics, physical science,
   physicochemistry, physicomathematics, physics, psychophysics,
   radiation physics, radionics, solar physics, solid-state physics,
   spectrometry, spectrophotometry, spectroscopy, statics,
   stereophysics, stereoscopy, telescopy, theoretical physics,
   thermodynamics, zoophysics