unbelievable
1. [ adjective ] beyond belief or understanding
Synonyms: incredible
Examples:

"at incredible speed" "the book's plot is simply incredible"

Related terms: credible improbable astounding undreamed fabulous unconvincing unthinkable incredulous implausible credibility
2. [ adjective ] having a probability to low to inspire belief
Synonyms: unconvincing unlikely improbable
Related terms: implausible
Similar spelling:   unbelievably
  unbeliever
  unbelieving
  unbelievingly