Source : Webster's Revised Unabridged Dictionary (1913)

Tenable \Ten"a*ble\, a. [F. tenable, fr. tenir to hold, L.
   tenere. See {Thin}, and cf. {Continue}, {Continent},
   {Entertain}, {Maintain}, {Tenant}, {Tent}.]
   Capable of being held, naintained, or defended, as against an
   assailant or objector, or againts attempts to take or
   process; as, a tenable fortress, a tenable argument.

         If you have hitherto concealed his sight, Let it be
         tenable in your silence still.           --Shak.

         I would be the last man in the world to give up his
         cause when it was tenable.               --Sir W.
                                                  Scott.

Source : WordNet®

tenable
     adj : based on sound reasoning or evidence; "a reasonable
           argument"; "well-founded suspicions" [syn: {well-founded}]