IPA: //ʌnˈspiːkəbl//
KK: /ʌnˈspiːkəbl/
Something that cannot be described in words, often because it is too extreme or terrible.
The horror of the situation was unspeakable, leaving everyone in shock.
Unspeakable → It is formed from "un-" (meaning not) and "speak" (from Old English "specan", meaning to say or talk) and "-able" (meaning capable of). The word "unspeakable" describes something that is not capable of being spoken about, often due to its extreme nature.
Think of something that is 'not' ('un-') able to be 'said' ('speak') — that's why unspeakable refers to things too terrible or extreme to talk about.