Source : Webster's Revised Unabridged Dictionary (1913)

Navigable \Nav"i*ga*ble\, a. [L. navigabilis: cf. F. navigable.
   See {Navigate}.]
   Capable of being navigated; deep enough and wide enough to
   afford passage to vessels; as, a navigable river.

   Note: By the comon law, a river is considered as navigable
         only so far as the tide ebbs and flows in it. This is
         also the doctrine in several of the United tates. In
         other States, the doctrine of thje civil law prevails,
         which is, that a navigable river is a river capable of
         being navigated, in the common sense of the term.
         --Kent. Burrill. -- {Nav"i*ga*ble*ness}, n. --
         {Nav"i*ga*bly}, adv.

Source : WordNet®

navigable
     adj : able to be sailed on or through safely; "navigable waters";
           "a navigable channel"