Not easily debunked

• Like a good argument or theory
• Like a well-armed fort
• Like an excellent argument
• Defensible points accepted by board
• Hard to dispute, as a theory
• Not like the Alamo
• Logical, as a theory (7)
• Can be maintained

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
"capable of being held or maintained," 1570s, from Middle French tenable , from Old French (12c.), from tenir "to hold," from Latin tenere "to hold, keep" (see tenet ).

Wikipedia Word definitions in Wikipedia