Source : Webster's Revised Unabridged Dictionary (1913)

Definable \De*fin"a*ble\, a. [From {Define}.]
   Capable of being defined, limited, or explained;
   determinable; describable by definition; ascertainable; as,
   definable limits; definable distinctions or regulations;
   definable words. -- {De*fin"a*bly}, adv.

Source : WordNet®

definable
     adj : capable of being defined, limited, or explained; "definable
           terms"; "definable rules"