Source : Webster's Revised Unabridged Dictionary (1913)

Excitable \Ex*cit"a*ble\, a. [L. excitabilis inciting: cf. F.
   excitable.]
   Capable of being excited, or roused into action; susceptible
   of excitement; easily stirred up, or stimulated.

Source : WordNet®

excitable
     adj 1: easily excited [ant: {unexcitable}]
     2: capable of responding to stimuli [syn: {irritable}]