tenab

a. [ F. tenable, fr. tenir to hold, L. tenere. See Thin, and cf. Continue, Continent, Entertain, Maintain, Tenant, Tent. ] Capable of being held, maintained, or defended, as against an assailant or objector, or against attempts to take or process; as, a tenable fortress, a tenable argument. [ 1913 Webster ]

If you have hitherto concealed his sight,
Let it be tenable in your silence still. Shak. [ 1913 Webster ]

I would be the last man in the world to give up his cause when it was tenable. Sir W. Scott. [ 1913 Webster ]