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.

Source: Webster's Revised Unabridged Dictionary (1913)