Source : Webster's Revised Unabridged Dictionary (1913)

Observable \Ob*serv"a*ble\, a. [L. observabilis: cf.F.
   observable.]
   Worthy or capable of being observed; discernible; noticeable;
   remarkable. --Sir. T. Browne.

         The difference is sufficiently observable. --Southey.
   -- {Ob*serv"a*ble*ness}, n. -- {Ob*serv"a*bly}, adv.

Source : WordNet®

observable
     adj : capable of being seen or noticed; "a discernible change in
           attitude"; "a clearly evident erasure in the
           manuscript"; "an observable change in behavior" [syn: {discernible},
            {evident}]