IPA: //ʌnˈoʊpənəbl//
KK: /ʌnˈoʊpənəbl/
Something that cannot be opened or accessed.
The box was unopenable, no matter how hard I tried.
Unopenable → It is formed from "un-" (meaning not) and "open" (from Old English "openian", meaning to make open) and "-able" (meaning capable of). The word "unopenable" means not capable of being opened.
Think of 'not' ('un-') being added to 'open' — this helps you remember that 'unopenable' means something that cannot be opened.