indemonstrable

adjective

in·​de·​mon·​stra·​ble ˌin-di-ˈmän(t)-strə-bəl 

(ˌ)in-ˈde-mən-strə-

: incapable of being demonstrated : not subject to proof

indemonstrably

ˌin-di-ˈmän(t)-strə-blē 

(ˌ)in-ˈde-mən-strə-

adverb

Word History

First Known Use

1570, in the meaning defined above