irresoluble

adjective

ir·​re·​sol·​u·​ble ˌir-i-ˈzäl-yə-bəl 

1

: having or admitting of no solution or explanation

an irresoluble question

2

archaic : indissoluble

Word History

Etymology

Latin irresolubilis, from in- + resolvere to resolve

First Known Use

1666, in the meaning defined at sense 2