The Collaborative International Dictionary of English v.0.48:

Attenuate \At*ten"u*ate\, v. i.
   To become thin, slender, or fine; to grow less; to lessen.
   [1913 Webster]

         The attention attenuates as its sphere contracts.
                                                  --Coleridge.
   [1913 Webster] Attenuate

The Collaborative International Dictionary of English v.0.48:

Attenuate \At*ten"u*ate\, Attenuated \At*ten"u*a`ted\, a. [L.
   attenuatus, p. p.]
   1. Made thin or slender.
      [1913 Webster]

   2. Made thin or less viscid; rarefied. --Bacon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Attenuate \At*ten"u*ate\, v. t. [imp. & p. p. Attenuated; p.
   pr. & vb. n. Attenuating.] [L. attenuatus, p. p. of
   attenuare; ad + tenuare to make thin, tenuis thin. See
   Thin.]
   1. To make thin or slender, as by mechanical or chemical
      action upon inanimate objects, or by the effects of
      starvation, disease, etc., upon living bodies.
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   2. To make thin or less consistent; to render less viscid or
      dense; to rarefy. Specifically: To subtilize, as the
      humors of the body, or to break them into finer parts.
      [1913 Webster]

   3. To lessen the amount, force, or value of; to make less
      complex; to weaken.
      [1913 Webster]

            To undersell our rivals . . . has led the
            manufacturer to . . . attenuate his processes, in
            the allotment of tasks, to an extreme point. --I.
                                                  Taylor.
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            We may reject and reject till we attenuate history
            into sapless meagerness.              --Sir F.
                                                  Palgrave.
      [1913 Webster]

WordNet (r) 3.0 (2006):

attenuate
    adj 1: reduced in strength; "the faded tones of an old
           recording" [syn: attenuate, attenuated, faded,
           weakened]
    v 1: weaken the consistency of (a chemical substance) [syn:
         rarefy, attenuate]
    2: become weaker, in strength, value, or magnitude