inconceivable

UK: /ˌɪnkənˈsiːvəb^əl/

US: /ˌɪnkənˈsivəbəl/

US: (in′kən sē′və bəl)

WordReference Random House Learner's Dictionary of American English © 2025

in•con•ceiv•a•ble /ˌɪnkənˈsivəbəl/   adj. 

1. that cannot be imagined:
   inconceivable distances.
   [it + be + ~ + that clause]
   It's inconceivable that we'll travel to distant galaxies.
2. incredible:
   inconceivable blunders.
   [it + be + ~ + that clause]
   It's inconceivable that these things should happen.
in•con•ceiv•ab•ly, adv. 

WordReference Random House Unabridged Dictionary of American English © 2025

in•con•ceiv•a•ble  (in′kən sē′və bəl), adj. 

1. not conceivable;
   unimaginable;
   unthinkable
2. unbelievable;
   incredible.

• in-³ + conceivable 1625–35

in′con•ceiv′a•bil′i•ty, in′con•ceiv′a•ble•ness, n. 
in′con•ceiv′a•bly, adv. 

Collins Concise English Dictionary © HarperCollins Publishers::

inconceivable / ˌɪnkənˈsiːvəb^əl/ adjective

1. incapable of being conceived, imagined, or considered

ˌinconˌceivaˈbility, ˌinconˈceivableness noun

ˌinconˈceivably adverb