tenable

Definitions:

That may be hold, maintained, or defended against an assailant or against attempts to take it.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)
That may be held; capable of being maintained or defended.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
That may be held or maintained.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)
Tenableness.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
Capable of being retained, kept, or defended.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Capable of being held or defended, as an argument.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Tenably.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)

Usage examples:

Yet there could be as little doubt that no other theory was tenable
- Project Gutenberg History of The Netherlands, 1555-1623, Complete by John Lothrop Motley
But probably it would be a good thing to exterminate them on the tenable ground that they are general menaces to the welfare of society."
- Mystery Ranch by Arthur Chapman
This wooden fortress, enclosing about three hundred fighting men with their families, held out several days; but no sooner had the heavy guns of the Russians effected a breach, than the besieged, finding their position no longer tenable surrendered at discretion, and delivered over the sons of their chiefs as hostages for their submission.
- A New Voyage Round the World, in the years 1823, 24, 25, and 26, Vol. 2 by Otto von Kotzebue