IPA: /ˌɪn.kənˈsiː.və.bəl/
KK: /ɪnˈkɒnsɪvəbəl/
Something that cannot be understood or imagined; it seems impossible or unbelievable.
The idea of flying cars in the near future seemed inconceivable to many people.
Inconceivable → It is formed from "in-" (meaning not) and "capi" (from Latin "capere", meaning to seize or take) and "-able" (meaning capable of). The word "inconceivable" means not capable of being seized or understood, thus referring to something that cannot be comprehended or imagined.
Think of something that is 'not' ('in-') able to be 'taken' or 'understood' ('capi') — that's why inconceivable means something that cannot be imagined.