tenable

adj. 1 maintainable or defensible against attack or objection (tenable position). 2 (foll. By for, by) (of an office etc.) That can be held for (a specified period) or by (a specified class of person).  tenability n. [french tenir hold]

a. 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.