Synonyms of the word 
INCONCEIVABLE → IMPOSSIBLE - UNIMAGINABLE - UNTHINKABLE
inconceivable
- adj. unable to be conceived, unbelievable.
impossible
- adj. Not possible; not able to be done or happen.
- adj. (colloquial, of a person) Very difficult to deal with.
- adj. (mathematics, dated) imaginary.
- n. (obsolete) an impossibility.
unimaginable
- adj. unable to be imagined; inconceivable or mind-boggling; beyond belief.
unthinkable
- adj. Incapable of being believed; incredible.
- adj. Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.
If you are interested in words, visit the following sites :
- wiktionary.org/inconceivable For complete definition of a word
- 1word.ws/inconceivable to play with words, suffixs, prefixs, etc.