IPA: //ʌnˈpæsəbl//
KK: /ʌnˈpæsəbl/
Something that cannot be crossed or traveled over.
The road was unpassable due to the heavy snowfall.
Unpassable → It is formed from "un-" (meaning not) and "passable" (from Latin "passabilis", meaning able to be passed). The word "unpassable" means not able to be passed or traversed.
Think of 'not' ('un-') being added to 'able to be passed' ('passable') — that's why unpassable means something that cannot be crossed.