Webster’s Revised Unabridged Dictionary · 1913
Tenable
Ten′a·ble (tĕn′ȧ·b'l), 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.