(a.) 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.

OK acceptable admissible agreeable all right alright arguable believable colorable conceivable condonable credible creditable defendable defensible excusable fiduciary good enough imaginable impregnable justifiable maintainable okay passable plausible possible rational reasonable reliable secure supportable trustworthy trusty unexceptionable unimpeachable unobjectionable unquestionable viable vindicable warrantable workable worthy of faith