Source : Webster's Revised Unabridged Dictionary (1913)

Attenuation \At*ten`u*a"tion\, n. [L. attenuatio: cf. F.
   att['e]nuation.]
   1. The act or process of making slender, or the state of
      being slender; emaciation.

   2. The act of attenuating; the act of making thin or less
      dense, or of rarefying, as fluids or gases.

   3. The process of weakening in intensity; diminution of
      virulence; as, the attenuation of virus.

Source : WordNet®

attenuation
     n 1: weakening in force or intensity; "attenuation in the volume
          of the sound" [syn: {fading}]
     2: the property of something that has been weakened or reduced
        in thickness or density

Source : Free On-Line Dictionary of Computing

attenuation
     
         The progressive reduction in {amplitude} of a
        signal as it travels farther from the point of origin.
     
        For example, an electric signal's amplitude reduces with
        distance due to electrical {impedance}.  Attenuation is
        usually measured in {decibels} [per metre?].
     
        Attenuation does not imply appreciable modification of the
        shape of the waveform (distortion), though as the signal
        amplitude falls the {signal-to-noise ratio} will also fall
        unless the channel itself is noise free or the signal is
        amplified at some intermediate point(s) along the channel.
     
        ["Networking Essentials, second edition",
        Microsoft Corporation, pub. Microsoft Press 1997].
     
        (2003-07-29)