The Collaborative International Dictionary of English v.0.48:

Susceptible \Sus*cep"ti*ble\, a. [F., from L. suscipere,
   susceptum, to take up, to support, undertake, recognize,
   admit; pref. sus (see Sub-) + capere to take. See
   Capable.]
   1. Capable of admitting anything additional, or any change,
      affection, or influence; readily acted upon; as, a body
      susceptible of color or of alteration.
      [1913 Webster]

            It sheds on souls susceptible of light,
            The glorious dawn of our eternal day. --Young.
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   2. Capable of impression; having nice sensibility;
      impressible; tender; sensitive; as, children are more
      susceptible than adults; a man of a susceptible heart.
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            Candidates are . . . not very susceptible of
            affronts.                             --Cowper.
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            I am constitutionally susceptible of noises. --Lamb.
      [1913 Webster] -- Sus*cep"ti*ble*ness, n. --
      Sus*cep"ti*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

susceptibleness
    n 1: the state of being susceptible; easily affected [syn:
         susceptibility, susceptibleness] [ant: immunity,
         unsusceptibility]