IPA: //ʌnˈʌtərəbəl//
KK: /ʌnˈʌtərəbəl/
Something that cannot be expressed in words or is too great to be described.
The beauty of the sunset was unutterable, leaving us speechless.
Unutterable → It is formed from "un-" (meaning not) and "utter" (from Old French *utrer*, meaning to speak or express) and "-able" (meaning capable of). The word "unutterable" means not capable of being expressed or spoken.
Think of something that cannot be 'spoken' ('utter') and remember that 'un-' means not, so 'unutterable' refers to something that cannot be expressed.