adj. capable of being maintained or justified; well-founded
adj. capable of being defended against assault or attack; defensible
the GNU version of the Collaborative International Dictionary of English
adj. Capable of being held, maintained, or defended, as against an assailant or objector, or against attempts to take or process.
The Century Dictionary and Cyclopedia
Capable of being held, maintained, or defended successfully against an assailant; successfully defensible against attacks or arguments or objections: as, a tenable fortress; a tenable theory.
Held; retained; kept secret or inviolate.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. based on sound reasoning or evidence
Word Usage
"What seems no longer tenable is the romantic, idealized idea of fatherhood once associated with “The Godfather,” where the passionate mutual devotion of fathers and sons seemed completely of a piece with the relentless pursuit of power and destruction of the enemy."