IPA: /ˌʌnɪˈmædʒɪnəbli/
KK: /ʌnɪˈmædʒɪnəbli/
In a way that is beyond what can be imagined or thought of.
The storm was unimaginably powerful, causing widespread destruction.
Unimaginably → It is formed from "un-" (meaning not), "imaginable" (from Latin "imaginabilis", meaning able to be imagined), and the suffix "-ly" (meaning in a manner). The word "unimaginably" means in a manner that is not able to be imagined or beyond imagination.
Think of 'not' ('un-') being added to 'able to be imagined' ('imaginable') — this helps you remember that 'unimaginably' describes something that is beyond what we can conceive.