From The Collaborative International Dictionary of English v.0.48 [gcide]:
Tenable \Ten"a*ble\ (t[e^]n"[.a]*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, 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]
From WordNet (r) 3.0 (2006) [wn]:
tenable
adj 1: based on sound reasoning or evidence; "well-founded
suspicions" [syn: tenable, well-founded]