The Collaborative International Dictionary of English v.0.48:

Palpable \Pal"pa*ble\, a. [F. palpable, L. palpabilis, fr.
   palpare to feel, stroke; cf. palpus the soft palm of the
   hand.]
   1. Capable of being touched and felt; perceptible by the
      touch; as, a palpable form. --Shak.
      [1913 Webster]

            Darkness must overshadow all his bounds,
            Palpable darkness.                    --Milton.
      [1913 Webster]

   2. Easily perceptible; plain; distinct; obvious; readily
      perceived and detected; gross; as, palpable imposture;
      palpable absurdity; palpable errors. "Three persons
      palpable." --P. Plowman.
      [1913 Webster]

            [Lies] gross as a mountain, open, palpable. --Shak.
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            A hit, A very palpable hit.           --Shak.
                                                  (Hamlet)
      [1913 Webster] -- Pal"pa*ble*ness, n. -- Pal"pa*bly,
      adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

palpably
    adv 1: so as to be palpable; "she was palpably nervous"