Source : Webster's Revised Unabridged Dictionary (1913)

Ether \E"ther\, n. [L. aether, Gr. ?, fr. ? to light up, kindle,
   burn, blaze; akin to Skr. idh, indh, and prob. to E. idle:
   cf. F. ['e]ther.] [Written also {[ae]ther}.]
   1. (Physics) A medium of great elasticity and extreme
      tenuity, supposed to pervade all space, the interior of
      solid bodies not excepted, and to be the medium of
      transmission of light and heat; hence often called
      {luminiferous ether}.