Meaning of anacoustic

an•a•cous•tic

Pronunciation: (an"u-k'stik), [key]
— adj.
  1. of or pertaining to the upper portion of the earth's atmosphere and to interplanetary space, where sound cannot be transmitted because molecules are too far apart to serve as a transmitting medium.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.