Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

optics
     n : the branch of physics that studies the physical properties
         of light