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.
      [1913 Webster]

   2. Capable of impression; having nice sensibility;
      impressible; tender; sensitive; as, children are more
      susceptible than adults; a man of a susceptible heart.
      [1913 Webster]

            Candidates are . . . not very susceptible of
            affronts.                             --Cowper.
      [1913 Webster]

            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):

susceptible
    adj 1: (often followed by `of' or `to') yielding readily to or
           capable of; "susceptible to colds"; "susceptible of
           proof" [ant: insusceptible, unsusceptible]
    2: easily impressed emotionally

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "susceptible":
   accessible, adaptable, affected, alive to, amenable,
   answerable for, apt, apt to, aroused, aware, bendable, bending,
   bright, capable of, clever, cognizant, compliant, conscious,
   delicate, dependent on, disposed, docile, ductile, educable,
   elastic, emotionable, exposed, exposed to, extensible, extensile,
   fabricable, facile, fictile, flexible, flexile, flexuous, formable,
   formative, giving, gullible, impressed, impressible,
   impressionable, impressive, in danger of, incident to, inclined,
   influenceable, influenced, instructable, intelligent, liable,
   liable to, like putty, likely to, limber, lissome, lithe,
   lithesome, malleable, moldable, motivated, movable, naive, naked,
   naked to, nonimmune, nonresistant, obliged to, obnoxious, open,
   open to, open-minded, passible, perceptive, persuadable,
   persuasible, pervious, plastic, pliable, pliant, predisposed,
   prone, prone to, quick, ready, ready for, receptive,
   responsible for, responsive, ripe for instruction, roused,
   schoolable, sensible, sensile, sensitive, sensitive to, sentient,
   sequacious, shapable, soft, softhearted, springy, standing to,
   stirred, suasible, subject, subject to, submissive, suggestible,
   supple, susceptive, susceptive to, swayable, swayed, sympathetic,
   teachable, tender, tenderhearted, thirsty for knowledge, touched,
   tractable, tractile, trainable, warmhearted, weak, whippy, willing,
   willowy, within range of, yielding